diff --git a/.dart_tool/package_config.json b/.dart_tool/package_config.json
index ef7591c4167..059a1e62afe 100644
--- a/.dart_tool/package_config.json
+++ b/.dart_tool/package_config.json
@@ -11,7 +11,7 @@
     "constraint, update this by running tools/generate_package_config.dart."
   ],
   "configVersion": 2,
-  "generated": "2021-04-13T13:32:11.977579",
+  "generated": "2021-04-14T10:32:11.514470",
   "generator": "tools/generate_package_config.dart",
   "packages": [
     {
@@ -749,7 +749,7 @@
       "name": "vm_snapshot_analysis",
       "rootUri": "../pkg/vm_snapshot_analysis",
       "packageUri": "lib/",
-      "languageVersion": "2.8"
+      "languageVersion": "2.12"
     },
     {
       "name": "wasm",
diff --git a/pkg/vm_snapshot_analysis/lib/ascii_table.dart b/pkg/vm_snapshot_analysis/lib/ascii_table.dart
index a0e54041832..37218146502 100644
--- a/pkg/vm_snapshot_analysis/lib/ascii_table.dart
+++ b/pkg/vm_snapshot_analysis/lib/ascii_table.dart
@@ -16,7 +16,7 @@ abstract class Row {
   /// Note: there is a border on the left and right of each column
   /// plus whitespace around it.
   static int totalWidth(List<int> widths) =>
-      widths.fold(0, (sum, width) => sum + width + 3) + 1;
+      widths.fold<int>(0, (sum, width) => sum + width + 3) + 1;
 }
 
 enum Separator {
@@ -91,7 +91,7 @@ class Text {
   final String value;
   final AlignmentDirection direction;
 
-  Text({this.value, this.direction});
+  Text({required this.value, required this.direction});
   Text.left(String value)
       : this(value: value, direction: AlignmentDirection.Left);
   Text.right(String value)
@@ -113,7 +113,6 @@ class Text {
         final diff = width - value.length;
         return ' ' * (diff ~/ 2) + value + (' ' * (diff - diff ~/ 2));
     }
-    return null; // Make analyzer happy.
   }
 
   int get length => value.length;
@@ -126,7 +125,7 @@ class AsciiTable {
 
   final List<Row> rows = <Row>[];
 
-  AsciiTable({List<dynamic> header, this.maxWidth = unlimitedWidth}) {
+  AsciiTable({List<dynamic>? header, this.maxWidth = unlimitedWidth}) {
     if (header != null) {
       addSeparator();
       addRow(header);
diff --git a/pkg/vm_snapshot_analysis/lib/instruction_sizes.dart b/pkg/vm_snapshot_analysis/lib/instruction_sizes.dart
index 635f8dd504f..a1db07f09d4 100644
--- a/pkg/vm_snapshot_analysis/lib/instruction_sizes.dart
+++ b/pkg/vm_snapshot_analysis/lib/instruction_sizes.dart
@@ -40,16 +40,20 @@ class SymbolInfo {
 
   /// If this instructions object originated from a function then [libraryUri]
   /// will contain uri of the library of that function.
-  final String libraryUri;
+  final String? libraryUri;
 
   /// If this instructions object originated from a function then [className]
   /// would contain name of the class owning that function.
-  final String className;
+  final String? className;
 
   /// Size of the instructions object in bytes.
   final int size;
 
-  SymbolInfo({String name, this.libraryUri, this.className, this.size})
+  SymbolInfo(
+      {required String name,
+      this.libraryUri,
+      this.className,
+      required this.size})
       : name = Name(name);
 
   static SymbolInfo _fromJson(Map<String, dynamic> map) {
@@ -74,37 +78,41 @@ ProgramInfo toProgramInfo(List<SymbolInfo> symbols,
   final program = ProgramInfo();
   for (var sym in symbols) {
     final scrubbed = sym.name.scrubbed;
-    if (sym.libraryUri == null) {
+    final libraryUri = sym.libraryUri;
+
+    // Handle stubs specially.
+    if (libraryUri == null) {
       assert(sym.name.isStub);
       final node = program.makeNode(
           name: scrubbed, parent: program.stubs, type: NodeType.functionNode);
       assert(node.size == null || sym.name.isTypeTestingStub);
       node.size = (node.size ?? 0) + sym.size;
-    } else {
-      // Split the name into components (names of individual functions).
-      final path = sym.name.components;
-
-      var node = program.root;
-      final package = packageOf(sym.libraryUri);
-      if (package != sym.libraryUri) {
-        node = program.makeNode(
-            name: package, parent: node, type: NodeType.packageNode);
-      }
-      node = program.makeNode(
-          name: sym.libraryUri, parent: node, type: NodeType.libraryNode);
-      node = program.makeNode(
-          name: sym.className, parent: node, type: NodeType.classNode);
-      node = program.makeNode(
-          name: path.first, parent: node, type: NodeType.functionNode);
-      for (var name in path.skip(1)) {
-        if (collapseAnonymousClosures) {
-          name = Name.collapse(name);
-        }
-        node = program.makeNode(
-            name: name, parent: node, type: NodeType.functionNode);
-      }
-      node.size = (node.size ?? 0) + sym.size;
+      continue;
     }
+
+    // Split the name into components (names of individual functions).
+    final path = sym.name.components;
+
+    var node = program.root;
+    final package = packageOf(libraryUri);
+    if (package != libraryUri) {
+      node = program.makeNode(
+          name: package, parent: node, type: NodeType.packageNode);
+    }
+    node = program.makeNode(
+        name: libraryUri, parent: node, type: NodeType.libraryNode);
+    node = program.makeNode(
+        name: sym.className!, parent: node, type: NodeType.classNode);
+    node = program.makeNode(
+        name: path.first, parent: node, type: NodeType.functionNode);
+    for (var name in path.skip(1)) {
+      if (collapseAnonymousClosures) {
+        name = Name.collapse(name);
+      }
+      node = program.makeNode(
+          name: name, parent: node, type: NodeType.functionNode);
+    }
+    node.size = (node.size ?? 0) + sym.size;
   }
 
   return program;
diff --git a/pkg/vm_snapshot_analysis/lib/name.dart b/pkg/vm_snapshot_analysis/lib/name.dart
index 3b17bd11190..5d4e569d84b 100644
--- a/pkg/vm_snapshot_analysis/lib/name.dart
+++ b/pkg/vm_snapshot_analysis/lib/name.dart
@@ -15,9 +15,6 @@ class Name {
   /// Raw textual representation of the name as it occurred in the output
   /// of the AOT compiler.
   final String raw;
-  String _scrubbed;
-
-  Name(this.raw);
 
   /// Pretty version of the name, with some of the irrelevant information
   /// removed from it.
@@ -26,16 +23,18 @@ class Name {
   /// so we are not removing any details that are used for disambiguation.
   /// The only exception are type testing stubs, these refer to type names
   /// and types names are not bound to be unique between compilations.
-  String get scrubbed => _scrubbed ??=
+  late final String scrubbed =
       raw.replaceAll(isStub ? _stubScrubbingRe : _scrubbingRe, '');
 
+  Name(this.raw);
+
   /// Returns true if this name refers to a stub.
   bool get isStub => raw.startsWith('[Stub] ');
 
   /// Returns true if this name refers to an allocation stub.
   bool get isAllocationStub => raw.startsWith('[Stub] Allocate ');
 
-  /// Returns ture if this name refers to a type testing stub.
+  /// Returns true if this name refers to a type testing stub.
   bool get isTypeTestingStub => raw.startsWith('[Stub] Type Test ');
 
   /// Split this name into individual '.' separated components (e.g. names of
diff --git a/pkg/vm_snapshot_analysis/lib/precompiler_trace.dart b/pkg/vm_snapshot_analysis/lib/precompiler_trace.dart
index 54d86fe765b..3c9843c249d 100644
--- a/pkg/vm_snapshot_analysis/lib/precompiler_trace.dart
+++ b/pkg/vm_snapshot_analysis/lib/precompiler_trace.dart
@@ -11,7 +11,8 @@ import 'package:vm_snapshot_analysis/program_info.dart';
 
 /// Build [CallGraph] based on the trace written by `--trace-precompiler-to`
 /// flag.
-CallGraph loadTrace(Object inputJson) => _TraceReader(inputJson).readTrace();
+CallGraph loadTrace(Object inputJson) =>
+    _TraceReader(inputJson as Map<String, dynamic>).readTrace();
 
 /// [CallGraphNode] represents a node of the call-graph. It can either be:
 ///
@@ -39,7 +40,7 @@ class CallGraphNode {
   /// Dominator of this node.
   ///
   /// Computed by [CallGraph.computeDominators].
-  CallGraphNode dominator;
+  late CallGraphNode dominator;
 
   /// Nodes dominated by this node.
   ///
@@ -99,13 +100,13 @@ class CallGraph {
 
   // Mapping from [ProgramInfoNode] to a corresponding [CallGraphNode] (if any)
   // via [ProgramInfoNode.id].
-  final List<CallGraphNode> _graphNodeByEntityId;
+  final List<CallGraphNode?> _graphNodeByEntityId;
 
   CallGraph._(this.program, this.nodes, this._graphNodeByEntityId);
 
   CallGraphNode get root => nodes.first;
 
-  CallGraphNode lookup(ProgramInfoNode node) => _graphNodeByEntityId[node.id];
+  CallGraphNode lookup(ProgramInfoNode node) => _graphNodeByEntityId[node.id]!;
 
   Iterable<CallGraphNode> get dynamicCalls =>
       nodes.where((n) => n.isDynamicCallNode);
@@ -113,7 +114,7 @@ class CallGraph {
   /// Compute a collapsed version of the call-graph, where
   CallGraph collapse(NodeType type, {bool dropCallNodes = false}) {
     final graphNodesByData = <Object, CallGraphNode>{};
-    final graphNodeByEntityId = <CallGraphNode>[];
+    final graphNodeByEntityId = <CallGraphNode?>[];
 
     ProgramInfoNode collapsed(ProgramInfoNode nn) {
       // Root always collapses onto itself.
@@ -127,7 +128,7 @@ class CallGraph {
       // hitting the root node.
       var n = nn;
       while (n.parent != program.root && n.type != type) {
-        n = n.parent;
+        n = n.parent!;
       }
       return n;
     }
@@ -186,14 +187,14 @@ class CallGraph {
 ///
 /// See README.md for description of the format.
 class _TraceReader {
-  final List<Object> trace;
-  final List<Object> strings;
-  final List<Object> entities;
+  final List<dynamic> trace;
+  final List<String> strings;
+  final List<dynamic> entities;
 
   final program = ProgramInfo();
 
   /// Mapping between entity ids and corresponding [ProgramInfoNode] nodes.
-  final entityById = List<ProgramInfoNode>.filled(1024, null, growable: true);
+  final entityById = List<ProgramInfoNode?>.filled(1024, null, growable: true);
 
   /// Mapping between functions (represented as [ProgramInfoNode]s) and
   /// their selector ids.
@@ -203,21 +204,22 @@ class _TraceReader {
   final dynamicFunctions = Set<ProgramInfoNode>();
 
   _TraceReader(Map<String, dynamic> data)
-      : strings = data['strings'],
+      : strings = (data['strings'] as List<dynamic>).cast<String>(),
         entities = data['entities'],
         trace = data['trace'];
 
   /// Read all trace events and construct the call graph based on them.
   CallGraph readTrace() {
     var pos = 0; // Position in the [trace] array.
-    CallGraphNode currentNode;
+    late CallGraphNode currentNode;
+    int maxId = 0;
 
     final nodes = <CallGraphNode>[];
-    final nodeByEntityId = <CallGraphNode>[];
+    final nodeByEntityId = <CallGraphNode?>[];
     final callNodesBySelector = <dynamic, CallGraphNode>{};
     final allocated = Set<ProgramInfoNode>();
 
-    Object next() => trace[pos++];
+    T next<T>() => trace[pos++] as T;
 
     CallGraphNode makeNode({dynamic data}) {
       final n = CallGraphNode(nodes.length, data: data);
@@ -232,6 +234,9 @@ class _TraceReader {
       if (nodeByEntityId.length <= n.id) {
         nodeByEntityId.length = n.id * 2 + 1;
       }
+      if (n.id > maxId) {
+        maxId = n.id;
+      }
       return nodeByEntityId[n.id] ??= makeNode(data: n);
     }
 
@@ -363,10 +368,13 @@ class _TraceReader {
   /// Read the entity at the given [index] in [entities].
   ProgramInfoNode readEntityAt(int index) {
     final type = entities[index];
+    final idx0 = entities[index + 1] as int;
+    final idx1 = entities[index + 2] as int;
+    final idx2 = entities[index + 3] as int;
     switch (type) {
       case 'C': // Class: 'C', <library-uri-idx>, <name-idx>, 0
-        final libraryUri = strings[entities[index + 1]];
-        final className = strings[entities[index + 2]];
+        final libraryUri = strings[idx0];
+        final className = strings[idx1];
 
         return program.makeNode(
             name: className,
@@ -375,9 +383,9 @@ class _TraceReader {
 
       case 'S':
       case 'F': // Function: 'F'|'S', <class-idx>, <name-idx>, <selector-id>
-        final classNode = getEntityAt(entities[index + 1]);
-        final functionName = strings[entities[index + 2]];
-        final int selectorId = entities[index + 3];
+        final classNode = getEntityAt(idx0);
+        final functionName = strings[idx1];
+        final int selectorId = idx2;
 
         final path = Name(functionName).rawComponents;
         if (path.last == 'FfiTrampoline') {
@@ -398,8 +406,8 @@ class _TraceReader {
         return node;
 
       case 'V': // Field: 'V', <class-idx>, <name-idx>, 0
-        final classNode = getEntityAt(entities[index + 1]);
-        final fieldName = strings[entities[index + 2]];
+        final classNode = getEntityAt(idx0);
+        final fieldName = strings[idx1];
 
         return program.makeNode(
             name: fieldName, parent: classNode, type: NodeType.other);
diff --git a/pkg/vm_snapshot_analysis/lib/program_info.dart b/pkg/vm_snapshot_analysis/lib/program_info.dart
index e24304875e3..cca2bca0cf9 100644
--- a/pkg/vm_snapshot_analysis/lib/program_info.dart
+++ b/pkg/vm_snapshot_analysis/lib/program_info.dart
@@ -5,8 +5,6 @@
 /// Classes for representing information about the program structure.
 library vm_snapshot_analysis.program_info;
 
-import 'package:meta/meta.dart';
-
 import 'package:vm_snapshot_analysis/v8_profile.dart';
 
 /// Represents information about compiled program.
@@ -22,7 +20,7 @@ class ProgramInfo {
 
   /// V8 snapshot profile if this [ProgramInfo] object was created from an
   /// output of `--write-v8-snapshot-profile-to=...` flag.
-  SnapshotInfo snapshotInfo;
+  SnapshotInfo? snapshotInfo;
 
   ProgramInfo._(this.root, this.stubs, this.unknown);
 
@@ -45,24 +43,22 @@ class ProgramInfo {
   }
 
   ProgramInfoNode makeNode(
-      {@required String name,
-      @required ProgramInfoNode parent,
-      @required NodeType type}) {
-    return parent.children.putIfAbsent(name, () {
-      final node = ProgramInfoNode._(
-          id: _nextId++, name: name, parent: parent ?? root, type: type);
-      node.parent.children[name] = node;
-      return node;
-    });
+      {required String name,
+      required ProgramInfoNode parent,
+      required NodeType type}) {
+    return parent.children.putIfAbsent(
+        name,
+        () => ProgramInfoNode._(
+            id: _nextId++, name: name, parent: parent, type: type));
   }
 
   /// Recursively visit all function nodes, which have [FunctionInfo.info]
   /// populated.
   void visit(
-      void Function(
-              String pkg, String lib, String cls, String fun, ProgramInfoNode n)
+      void Function(String? pkg, String lib, String? cls, String? fun,
+              ProgramInfoNode n)
           callback) {
-    final context = List<String>.filled(NodeType.values.length, null);
+    final context = List<String?>.filled(NodeType.values.length, null);
 
     void recurse(ProgramInfoNode node) {
       final prevContext = context[node._type];
@@ -72,11 +68,11 @@ class ProgramInfo {
         context[node._type] = node.name;
       }
 
-      final String pkg = context[NodeType.packageNode.index];
-      final String lib = context[NodeType.libraryNode.index];
-      final String cls = context[NodeType.classNode.index];
-      final String mem = context[NodeType.functionNode.index];
-      callback(pkg, lib, cls, mem, node);
+      final pkg = context[NodeType.packageNode.index];
+      final lib = context[NodeType.libraryNode.index];
+      final cls = context[NodeType.classNode.index];
+      final mem = context[NodeType.functionNode.index];
+      callback(pkg, lib!, cls, mem, node);
 
       for (var child in node.children.values) {
         recurse(child);
@@ -96,12 +92,14 @@ class ProgramInfo {
   Map<String, dynamic> toJson() => root.toJson();
 
   /// Lookup a node in the program given a path to it.
-  ProgramInfoNode lookup(List<String> path) {
+  ProgramInfoNode? lookup(List<String> path) {
     var n = root;
     for (var p in path) {
-      if ((n = n.children[p]) == null) {
-        break;
+      final next = n.children[p];
+      if (next == null) {
+        return null;
       }
+      n = next;
     }
     return n;
   }
@@ -121,12 +119,12 @@ String _typeToJson(NodeType type) => const {
       NodeType.classNode: 'class',
       NodeType.functionNode: 'function',
       NodeType.other: 'other',
-    }[type];
+    }[type]!;
 
 class ProgramInfoNode {
   final int id;
   final String name;
-  final ProgramInfoNode parent;
+  final ProgramInfoNode? parent;
   final Map<String, ProgramInfoNode> children = {};
   final int _type;
 
@@ -151,13 +149,13 @@ class ProgramInfoNode {
   /// Assuming that both `C.f` and `C.g` are included into AOT snapshot
   /// and string `"something"` does not occur anywhere else in the program
   /// then the size of `"something"` is going to be attributed to `C`.
-  int size;
+  int? size;
 
   ProgramInfoNode._(
-      {@required this.id,
-      @required this.name,
-      @required this.parent,
-      @required NodeType type})
+      {required this.id,
+      required this.name,
+      required this.parent,
+      required NodeType type})
       : _type = type.index;
 
   NodeType get type => NodeType.values[_type];
@@ -175,9 +173,10 @@ class ProgramInfoNode {
     var prefix = '';
     // Do not include root name or package name (library uri already contains
     // package name).
-    if (parent?.parent != null && parent?.type != NodeType.packageNode) {
-      prefix = parent.qualifiedName;
-      if (parent.type != NodeType.libraryNode) {
+    final p = parent;
+    if (p != null && p.parent != null && p.type != NodeType.packageNode) {
+      prefix = p.qualifiedName;
+      if (p.type != NodeType.libraryNode) {
         prefix += '.';
       } else {
         prefix += '::';
@@ -198,7 +197,7 @@ class ProgramInfoNode {
     var n = this;
     while (n.parent != null) {
       result.add(n.name);
-      n = n.parent;
+      n = n.parent!;
     }
     return result.reversed.toList();
   }
@@ -215,24 +214,24 @@ ProgramInfo computeDiff(ProgramInfo oldInfo, ProgramInfo newInfo) {
   final programDiff = ProgramInfo();
 
   var path = <Object>[];
-  void recurse(ProgramInfoNode oldNode, ProgramInfoNode newNode) {
+  void recurse(ProgramInfoNode? oldNode, ProgramInfoNode? newNode) {
     if (oldNode?.size != newNode?.size) {
       var diffNode = programDiff.root;
       for (var i = 0; i < path.length; i += 2) {
-        final name = path[i];
-        final type = path[i + 1];
+        final name = path[i] as String;
+        final type = path[i + 1] as NodeType;
         diffNode =
             programDiff.makeNode(name: name, parent: diffNode, type: type);
       }
-      diffNode.size ??= 0;
-      diffNode.size += (newNode?.size ?? 0) - (oldNode?.size ?? 0);
+      diffNode.size =
+          (diffNode.size ?? 0) + (newNode?.size ?? 0) - (oldNode?.size ?? 0);
     }
 
     for (var key in _allKeys(newNode?.children, oldNode?.children)) {
       final newChildNode = newNode != null ? newNode.children[key] : null;
       final oldChildNode = oldNode != null ? oldNode.children[key] : null;
       path.add(key);
-      path.add(oldChildNode?.type ?? newChildNode?.type);
+      path.add((oldChildNode?.type ?? newChildNode?.type)!);
       recurse(oldChildNode, newChildNode);
       path.removeLast();
       path.removeLast();
@@ -244,7 +243,7 @@ ProgramInfo computeDiff(ProgramInfo oldInfo, ProgramInfo newInfo) {
   return programDiff;
 }
 
-Iterable<T> _allKeys<T>(Map<T, dynamic> a, Map<T, dynamic> b) {
+Iterable<T> _allKeys<T>(Map<T, dynamic>? a, Map<T, dynamic>? b) {
   return <T>{...?a?.keys, ...?b?.keys};
 }
 
@@ -267,14 +266,14 @@ class Histogram {
 
   Histogram._(this.bucketInfo, this.buckets)
       : bySize = buckets.keys.toList(growable: false)
-          ..sort((a, b) => buckets[b] - buckets[a]),
+          ..sort((a, b) => buckets[b]! - buckets[a]!),
         totalSize = buckets.values.fold(0, (sum, size) => sum + size);
 
   static Histogram fromIterable<T>(
     Iterable<T> entries, {
-    @required int Function(T) sizeOf,
-    @required String Function(T) bucketFor,
-    @required BucketInfo bucketInfo,
+    required int Function(T) sizeOf,
+    required String Function(T) bucketFor,
+    required BucketInfo bucketInfo,
   }) {
     final buckets = <String, int>{};
 
@@ -290,20 +289,26 @@ class Histogram {
   /// Rebuckets the histogram given the new bucketing rule.
   Histogram map(String Function(String) bucketFor) {
     return Histogram.fromIterable(buckets.keys,
-        sizeOf: (key) => buckets[key],
+        sizeOf: (key) => buckets[key]!,
         bucketFor: bucketFor,
         bucketInfo: bucketInfo);
   }
 }
 
 /// Construct the histogram of specific [type] given a [ProgramInfo].
+///
+/// [filter] glob can be provided to skip some of the nodes in the [info]:
+/// a string is created which contains library name, class name and function
+/// name for the given node and if this string does not match the [filter]
+/// glob then this node is ignored.
 Histogram computeHistogram(ProgramInfo info, HistogramType type,
-    {String filter}) {
-  bool Function(String, String, String) matchesFilter;
+    {String? filter}) {
+  bool Function(String, String?, String?) matchesFilter;
 
   if (filter != null) {
     final re = RegExp(filter.replaceAll('*', '.*'), caseSensitive: false);
-    matchesFilter = (lib, cls, fun) => re.hasMatch("${lib}::${cls}.${fun}");
+    matchesFilter =
+        (lib, cls, fun) => re.hasMatch("${lib}::${cls ?? ''}.${fun ?? ''}");
   } else {
     matchesFilter = (_, __, ___) => true;
   }
@@ -318,10 +323,12 @@ Histogram computeHistogram(ProgramInfo info, HistogramType type,
       });
     }
 
+    final snapshotInfo = info.snapshotInfo!;
+
     return Histogram.fromIterable<Node>(
-        info.snapshotInfo.snapshot.nodes.where((n) =>
+        snapshotInfo.snapshot.nodes.where((n) =>
             filter == null ||
-            filteredNodes.contains(info.snapshotInfo.ownerOf(n).id)),
+            filteredNodes.contains(snapshotInfo.ownerOf(n).id)),
         sizeOf: (n) {
           return n.selfSize;
         },
@@ -329,17 +336,18 @@ Histogram computeHistogram(ProgramInfo info, HistogramType type,
         bucketInfo: const BucketInfo(nameComponents: ['Type']));
   } else {
     final buckets = <String, int>{};
-    final bucketing = Bucketing._forType[type];
+    final bucketing = Bucketing._forType[type]!;
 
     info.visit((pkg, lib, cls, fun, node) {
-      if (node.size == null || node.size == 0) {
+      final sz = node.size;
+      if (sz == null || sz == 0) {
         return;
       }
       if (!matchesFilter(lib, cls, fun)) {
         return;
       }
       final bucket = bucketing.bucketFor(pkg, lib, cls, fun);
-      buckets[bucket] = (buckets[bucket] ?? 0) + node.size;
+      buckets[bucket] = (buckets[bucket] ?? 0) + sz;
     });
 
     return Histogram._(bucketing, buckets);
@@ -363,15 +371,15 @@ class BucketInfo {
   /// one returned by [nameComponents]).
   List<String> namesFromBucket(String bucket) => [bucket];
 
-  const BucketInfo({@required this.nameComponents});
+  const BucketInfo({required this.nameComponents});
 }
 
 abstract class Bucketing extends BucketInfo {
   /// Constructs the bucket name from the given library name [lib], class name
   /// [cls] and function name [fun].
-  String bucketFor(String pkg, String lib, String cls, String fun);
+  String bucketFor(String? pkg, String lib, String? cls, String? fun);
 
-  const Bucketing({@required List<String> nameComponents})
+  const Bucketing({required List<String> nameComponents})
       : super(nameComponents: nameComponents);
 
   static const _forType = {
@@ -387,11 +395,11 @@ const String _nameSeparator = ';;;';
 
 class _BucketBySymbol extends Bucketing {
   @override
-  String bucketFor(String pkg, String lib, String cls, String fun) {
+  String bucketFor(String? pkg, String lib, String? cls, String? fun) {
     if (fun == null) {
       return '@other${_nameSeparator}';
     }
-    return '$lib${_nameSeparator}${cls}${cls != '' ? '.' : ''}${fun}';
+    return '$lib${_nameSeparator}${cls ?? ''}${cls != '' && cls != null ? '.' : ''}${fun}';
   }
 
   @override
@@ -402,7 +410,7 @@ class _BucketBySymbol extends Bucketing {
 
 class _BucketByClass extends Bucketing {
   @override
-  String bucketFor(String pkg, String lib, String cls, String fun) {
+  String bucketFor(String? pkg, String lib, String? cls, String? fun) {
     if (cls == null) {
       return '@other${_nameSeparator}';
     }
@@ -417,14 +425,14 @@ class _BucketByClass extends Bucketing {
 
 class _BucketByLibrary extends Bucketing {
   @override
-  String bucketFor(String pkg, String lib, String cls, String fun) => '$lib';
+  String bucketFor(String? pkg, String lib, String? cls, String? fun) => '$lib';
 
   const _BucketByLibrary() : super(nameComponents: const ['Library']);
 }
 
 class _BucketByPackage extends Bucketing {
   @override
-  String bucketFor(String pkg, String lib, String cls, String fun) =>
+  String bucketFor(String? pkg, String lib, String? cls, String? fun) =>
       pkg ?? lib;
 
   const _BucketByPackage() : super(nameComponents: const ['Package']);
diff --git a/pkg/vm_snapshot_analysis/lib/src/commands/compare.dart b/pkg/vm_snapshot_analysis/lib/src/commands/compare.dart
index 4a9442e01c7..bb2bdaff248 100644
--- a/pkg/vm_snapshot_analysis/lib/src/commands/compare.dart
+++ b/pkg/vm_snapshot_analysis/lib/src/commands/compare.dart
@@ -64,23 +64,25 @@ precisely based on their source position (which is included in their name).
 
   @override
   Future<void> run() async {
-    if (argResults.rest.length != 2) {
+    final args = argResults!;
+
+    if (args.rest.length != 2) {
       usageException('Need to provide path to old.json and new.json reports.');
     }
 
-    final columnWidth = argResults['column-width'];
+    final columnWidth = args['column-width'];
     final maxWidth = int.tryParse(columnWidth);
     if (maxWidth == null) {
       usageException(
           'Specified column width (${columnWidth}) is not an integer');
     }
 
-    final oldJsonPath = _checkExists(argResults.rest[0]);
-    final newJsonPath = _checkExists(argResults.rest[1]);
+    final oldJsonPath = _checkExists(args.rest[0]);
+    final newJsonPath = _checkExists(args.rest[1]);
     printComparison(oldJsonPath, newJsonPath,
         maxWidth: maxWidth,
-        granularity: _parseHistogramType(argResults['by']),
-        collapseAnonymousClosures: argResults['collapse-anonymous-closures']);
+        granularity: _parseHistogramType(args['by']),
+        collapseAnonymousClosures: args['collapse-anonymous-closures']);
   }
 
   HistogramType _parseHistogramType(String value) {
@@ -93,8 +95,9 @@ precisely based on their source position (which is included in their name).
         return HistogramType.byLibrary;
       case 'package':
         return HistogramType.byPackage;
+      default:
+        usageException('Unrecognized histogram type $value');
     }
-    return null;
   }
 
   File _checkExists(String path) {
@@ -136,10 +139,10 @@ precisely based on their source position (which is included in their name).
     printHistogram(diff, histogram,
         sizeHeader: 'Diff (Bytes)',
         prefix: histogram.bySize
-            .where((k) => histogram.buckets[k] > 0)
+            .where((k) => histogram.buckets[k]! > 0)
             .take(numLargerSymbolsToReport),
         suffix: histogram.bySize.reversed
-            .where((k) => histogram.buckets[k] < 0)
+            .where((k) => histogram.buckets[k]! < 0)
             .take(numSmallerSymbolsToReport)
             .toList()
             .reversed,
@@ -159,7 +162,7 @@ precisely based on their source position (which is included in their name).
       final newTypeHistogram =
           computeHistogram(newSizes, HistogramType.byNodeType);
 
-      final diffTypeHistogram = Histogram.fromIterable(
+      final diffTypeHistogram = Histogram.fromIterable<String>(
           Set<String>()
             ..addAll(oldTypeHistogram.buckets.keys)
             ..addAll(newTypeHistogram.buckets.keys),
diff --git a/pkg/vm_snapshot_analysis/lib/src/commands/explain.dart b/pkg/vm_snapshot_analysis/lib/src/commands/explain.dart
index 33c141803b7..e81833f4802 100644
--- a/pkg/vm_snapshot_analysis/lib/src/commands/explain.dart
+++ b/pkg/vm_snapshot_analysis/lib/src/commands/explain.dart
@@ -53,13 +53,15 @@ precompiler trace (an output of --trace-precompiler-to flag).
 
   @override
   Future<void> run() async {
-    final sizesJson = File(argResults.rest[0]);
+    final args = argResults!;
+
+    final sizesJson = File(args.rest[0]);
     if (!sizesJson.existsSync()) {
       usageException('Size profile ${sizesJson.path} does not exist!');
     }
     final sizesJsonRaw = await loadJsonFromFile(sizesJson);
 
-    final traceJson = File(argResults.rest[1]);
+    final traceJson = File(args.rest[1]);
     if (!traceJson.existsSync()) {
       usageException('Size profile ${traceJson.path} does not exist!');
     }
@@ -103,7 +105,7 @@ precompiler trace (an output of --trace-precompiler-to flag).
     }, bucketInfo: BucketInfo(nameComponents: ['Selector']));
 
     printHistogram(programInfo, histogram,
-        prefix: histogram.bySize.where((key) => histogram.buckets[key] > 0));
+        prefix: histogram.bySize.where((key) => histogram.buckets[key]! > 0));
 
     // For top 10 dynamic selectors print the functions which contain these
     // dynamic calls.
diff --git a/pkg/vm_snapshot_analysis/lib/src/commands/summary.dart b/pkg/vm_snapshot_analysis/lib/src/commands/summary.dart
index 13854d29a3b..90b87b9c0b7 100644
--- a/pkg/vm_snapshot_analysis/lib/src/commands/summary.dart
+++ b/pkg/vm_snapshot_analysis/lib/src/commands/summary.dart
@@ -12,7 +12,6 @@ import 'dart:io';
 import 'dart:math' as math;
 
 import 'package:args/command_runner.dart';
-import 'package:meta/meta.dart';
 
 import 'package:vm_snapshot_analysis/ascii_table.dart';
 import 'package:vm_snapshot_analysis/precompiler_trace.dart';
@@ -95,18 +94,20 @@ precisely based on their source position (which is included in their name).
 
   @override
   Future<void> run() async {
-    if (argResults.rest.length != 1) {
+    final args = argResults!;
+
+    if (args.rest.length != 1) {
       usageException('Need to specify input JSON.');
     }
 
-    final input = File(argResults.rest[0]);
+    final input = File(args.rest[0]);
     if (!input.existsSync()) {
       usageException('Input file ${input.path} does not exist!');
     }
 
-    final granularity = _parseHistogramType(argResults['by']);
+    final granularity = _parseHistogramType(args['by']);
 
-    final traceJson = argResults['precompiler-trace'];
+    final traceJson = args['precompiler-trace'];
     if (traceJson != null) {
       if (!File(traceJson).existsSync()) {
         usageException('Trace ${traceJson} does not exist!');
@@ -119,21 +120,21 @@ precisely based on their source position (which is included in their name).
       }
     }
 
-    final columnWidth = argResults['column-width'];
+    final columnWidth = args['column-width'];
     final maxWidth = int.tryParse(columnWidth);
     if (maxWidth == null) {
       usageException(
           'Specified column width (${columnWidth}) is not an integer');
     }
 
-    final depsStartDepthStr = argResults['deps-start-depth'];
+    final depsStartDepthStr = args['deps-start-depth'];
     final depsStartDepth = int.tryParse(depsStartDepthStr);
     if (depsStartDepth == null) {
       usageException('Specified depsStartDepth (${depsStartDepthStr})'
           ' is not an integer');
     }
 
-    final depsDisplayDepthStr = argResults['deps-display-depth'];
+    final depsDisplayDepthStr = args['deps-display-depth'];
     final depsDisplayDepth = int.tryParse(depsDisplayDepthStr);
     if (depsDisplayDepth == null) {
       usageException('Specified depsDisplayDepth (${depsStartDepthStr})'
@@ -143,14 +144,14 @@ precisely based on their source position (which is included in their name).
     await outputSummary(input,
         maxWidth: maxWidth,
         granularity: granularity,
-        collapseAnonymousClosures: argResults['collapse-anonymous-closures'],
-        filter: argResults['where'],
+        collapseAnonymousClosures: args['collapse-anonymous-closures'],
+        filter: args['where'],
         traceJson: traceJson != null ? File(traceJson) : null,
         depsStartDepth: depsStartDepth,
         depsDisplayDepth: depsDisplayDepth);
   }
 
-  static HistogramType _parseHistogramType(String value) {
+  HistogramType _parseHistogramType(String value) {
     switch (value) {
       case 'method':
         return HistogramType.bySymbol;
@@ -160,17 +161,18 @@ precisely based on their source position (which is included in their name).
         return HistogramType.byLibrary;
       case 'package':
         return HistogramType.byPackage;
+      default:
+        usageException('Unrecognized histogram type $value');
     }
-    return null;
   }
 }
 
-void outputSummary(File input,
+Future<void> outputSummary(File input,
     {int maxWidth = 0,
     bool collapseAnonymousClosures = false,
     HistogramType granularity = HistogramType.bySymbol,
-    String filter,
-    File traceJson,
+    String? filter,
+    File? traceJson,
     int depsStartDepth = 2,
     int depsDisplayDepth = 4,
     int topToReport = 30}) async {
@@ -182,7 +184,7 @@ void outputSummary(File input,
 
   // If precompiler trace is provided, collapse entries based on the dependency
   // graph (dominator tree) extracted from the trace.
-  void Function() printDependencyTrees;
+  void Function()? printDependencyTrees;
   if (traceJson != null &&
       (granularity == HistogramType.byLibrary ||
           granularity == HistogramType.byPackage)) {
@@ -235,8 +237,8 @@ void outputSummary(File input,
       var totalCount = 1;
       for (var n in node.dominated) {
         computeTotalsRecursively(n);
-        totalSize += totalSizes[n.data.name];
-        totalCount += totalCounts[n.data.name];
+        totalSize += totalSizes[n.data.name]!;
+        totalCount += totalCounts[n.data.name]!;
       }
       totalSizes[node.data.name] = totalSize;
       totalCounts[node.data.name] = totalCount;
@@ -255,7 +257,7 @@ void outputSummary(File input,
       final collapsedEntries = histogram.bySize
           .take(topToReport)
           .map((k) => collapsed[k])
-          .where((n) => n != null);
+          .whereType<CallGraphNode>();
       if (collapsedEntries.isNotEmpty) {
         print('\bDependency trees:');
         for (var n in collapsedEntries) {
@@ -302,9 +304,9 @@ void outputSummary(File input,
 void _printDominatedNodes(CallGraphNode node,
     {int displayDepth = 4,
     int maxChildrenToPrint = 10,
-    List<bool> isLastPerLevel,
-    @required Map<String, int> totalSizes,
-    @required Map<String, int> totalCounts}) {
+    List<bool>? isLastPerLevel,
+    required Map<String, int> totalSizes,
+    required Map<String, int> totalCounts}) {
   isLastPerLevel ??= [];
 
   // Subtract one to account for the parent node that is printed before the
@@ -315,8 +317,8 @@ void _printDominatedNodes(CallGraphNode node,
 
   final sizes = node.dominated.map((n) => totalSizes[n.data.name]).toList();
   final order = List.generate(node.dominated.length, (i) => i)
-    ..sort((a, b) => sizes[b] - sizes[a]);
-  final lastIndex = order.lastIndexWhere((i) => sizes[i] > 0);
+    ..sort((a, b) => sizes[b]! - sizes[a]!);
+  final lastIndex = order.lastIndexWhere((i) => sizes[i]! > 0);
 
   for (var j = 0, n = math.min(maxChildrenToPrint - 1, lastIndex);
       j <= n;
@@ -339,7 +341,7 @@ void _printDominatedNodes(CallGraphNode node,
   if (maxChildrenToPrint < lastIndex) {
     isLastPerLevel.add(true);
     print(
-        '${_treeLines(isLastPerLevel)} ... (+${totalCounts[node.data.name] - 1} deps)');
+        '${_treeLines(isLastPerLevel)} ... (+${totalCounts[node.data.name]! - 1} deps)');
     isLastPerLevel.removeLast();
   }
 }
diff --git a/pkg/vm_snapshot_analysis/lib/src/commands/treemap.dart b/pkg/vm_snapshot_analysis/lib/src/commands/treemap.dart
index 059d3532e47..2de0694dd55 100644
--- a/pkg/vm_snapshot_analysis/lib/src/commands/treemap.dart
+++ b/pkg/vm_snapshot_analysis/lib/src/commands/treemap.dart
@@ -56,24 +56,27 @@ viewed in a browser:
 
   @override
   Future<void> run() async {
-    if (argResults.rest.length != 2) {
+    final args = argResults!;
+
+    if (args.rest.length != 2) {
       usageException('Need to specify input JSON and output directory.');
     }
 
-    final input = File(argResults.rest[0]);
-    final outputDir = Directory(argResults.rest[1]);
+    final input = File(args.rest[0]);
+    final outputDir = Directory(args.rest[1]);
 
     if (!input.existsSync()) {
       usageException('Input file ${input.path} does not exist!');
     }
 
-    if (outputDir.existsSync() && !argResults['force']) {
+    if (outputDir.existsSync() && !args['force']) {
       usageException(
           'Output directory ${outputDir.path} already exists, specify --force to ignore.');
     }
 
     await generateTreeMap(input, outputDir,
-        format: _formatFromString[argResults['format']]);
+        format: _formatFromString[args['format']] ??
+            (throw 'Unrecognized format ${args['format']}'));
   }
 
   // Note: the first key in this map is the default format.
@@ -95,8 +98,8 @@ Future<void> generateTreeMap(File input, Directory outputDir,
   // Create output directory and copy all auxiliary files from binary_size tool.
   await outputDir.create(recursive: true);
 
-  final assetsUri = await Isolate.resolvePackageUri(
-      Uri.parse('package:vm_snapshot_analysis/src/assets'));
+  final assetsUri = (await Isolate.resolvePackageUri(
+      Uri.parse('package:vm_snapshot_analysis/src/assets')))!;
   final assetsDir = assetsUri.toFilePath();
   final d3SrcDir = p.join(assetsDir, 'd3', 'src');
 
@@ -114,7 +117,7 @@ Future<void> generateTreeMap(File input, Directory outputDir,
   final dataJsPath = p.join(outputDir.path, 'data.js');
   final sink = File(dataJsPath).openWrite();
   sink.write('var tree_data=');
-  await sink.addStream(Stream<Object>.fromIterable([tree])
+  await sink.addStream(Stream<Object?>.fromIterable([tree])
       .transform(json.encoder.fuse(utf8.encoder)));
   await sink.close();
 
diff --git a/pkg/vm_snapshot_analysis/lib/src/commands/utils.dart b/pkg/vm_snapshot_analysis/lib/src/commands/utils.dart
index f6a5bbe2f71..c73dab8b424 100644
--- a/pkg/vm_snapshot_analysis/lib/src/commands/utils.dart
+++ b/pkg/vm_snapshot_analysis/lib/src/commands/utils.dart
@@ -6,9 +6,9 @@ import 'dart:convert';
 import 'dart:io';
 
 Future<Object> loadJsonFromFile(File input) async {
-  return await input
+  return (await input
       .openRead()
       .transform(utf8.decoder)
       .transform(json.decoder)
-      .first;
+      .first)!;
 }
diff --git a/pkg/vm_snapshot_analysis/lib/src/dominators.dart b/pkg/vm_snapshot_analysis/lib/src/dominators.dart
index 5e9078f5921..92504f3dbb8 100644
--- a/pkg/vm_snapshot_analysis/lib/src/dominators.dart
+++ b/pkg/vm_snapshot_analysis/lib/src/dominators.dart
@@ -13,16 +13,16 @@ import 'dart:math' as math;
 /// native compiler (see runtime/vm/compiler/backend/flow_graph.cc).
 @pragma('vm:prefer-inline')
 List<int> computeDominators({
-  int size,
-  int root,
-  Iterable<int> succ(int n),
-  Iterable<int> predOf(int n),
-  void handleEdge(int from, int to),
+  required int size,
+  required int root,
+  required Iterable<int> Function(int) succ,
+  required Iterable<int> Function(int) predOf,
+  required void handleEdge(int from, int to),
 }) {
   // Compute preorder numbering for the graph using DFS.
   final parent = List<int>.filled(size, -1);
-  final preorder = List<int>.filled(size, null);
-  final preorderNumber = List<int>.filled(size, null);
+  final preorder = List<int>.filled(size, -1);
+  final preorderNumber = List<int>.filled(size, -1);
 
   var N = 0;
   void dfs() {
@@ -32,7 +32,7 @@ List<int> computeDominators({
       final p = s.p;
       final n = s.n;
       handleEdge(s.n, s.p);
-      if (preorderNumber[n] == null) {
+      if (preorderNumber[n] == -1) {
         preorderNumber[n] = N;
         preorder[preorderNumber[n]] = n;
         parent[preorderNumber[n]] = p;
@@ -122,5 +122,5 @@ List<int> computeDominators({
 class _DfsState {
   final int p;
   final int n;
-  _DfsState({this.p, this.n});
+  _DfsState({required this.p, required this.n});
 }
diff --git a/pkg/vm_snapshot_analysis/lib/treemap.dart b/pkg/vm_snapshot_analysis/lib/treemap.dart
index c0535e7a6c8..2d6da720ad8 100644
--- a/pkg/vm_snapshot_analysis/lib/treemap.dart
+++ b/pkg/vm_snapshot_analysis/lib/treemap.dart
@@ -82,10 +82,11 @@ Map<String, dynamic> treemapFromJson(Object inputJson,
   final root = {'n': '', 'children': {}, 'k': kindPath, 'maxDepth': 0};
 
   if (v8_profile.Snapshot.isV8HeapSnapshot(inputJson)) {
-    _treemapFromSnapshot(root, v8_profile.Snapshot.fromJson(inputJson),
+    _treemapFromSnapshot(
+        root, v8_profile.Snapshot.fromJson(inputJson as Map<String, dynamic>),
         format: format);
   } else {
-    final symbols = instruction_sizes.fromJson(inputJson);
+    final symbols = instruction_sizes.fromJson(inputJson as List<dynamic>);
     for (var symbol in symbols) {
       _addSymbol(root, _treePath(symbol), symbol.name.scrubbed, symbol.size);
     }
@@ -163,20 +164,22 @@ void _treemapFromSnapshot(Map<String, dynamic> root, v8_profile.Snapshot snap,
     return;
   }
 
+  final snapshotInfo = info.snapshotInfo!;
+
   final ownerPathCache =
-      List<String>.filled(info.snapshotInfo.infoNodes.length, null);
+      List<String?>.filled(snapshotInfo.infoNodes.length, null);
   ownerPathCache[info.root.id] = info.root.name;
 
   String ownerPath(ProgramInfoNode n) {
-    return ownerPathCache[n.id] ??=
-        ((n.parent != info.root) ? '${ownerPath(n.parent)}/${n.name}' : n.name);
+    return ownerPathCache[n.id] ??= ((n.parent != info.root)
+        ? '${ownerPath(n.parent!)}/${n.name}'
+        : n.name);
   }
 
-  final nameFormatter = _nameFormatters[format];
-
+  final nameFormatter = _nameFormatters[format]!;
   for (var node in snap.nodes) {
     if (node.selfSize > 0) {
-      final owner = info.snapshotInfo.ownerOf(node);
+      final owner = snapshotInfo.ownerOf(node);
 
       final name = nameFormatter(node);
       final path = ownerPath(owner);
@@ -227,7 +230,7 @@ Map<String, dynamic> _addChild(
 }
 
 /// Add the given symbol to the tree.
-void _addSymbol(Map<String, dynamic> root, String path, String name, int size,
+void _addSymbol(Map<String, dynamic> root, String path, String name, int? size,
     {String symbolType = symbolTypeGlobalText}) {
   if (size == null || size == 0) {
     return;
diff --git a/pkg/vm_snapshot_analysis/lib/utils.dart b/pkg/vm_snapshot_analysis/lib/utils.dart
index abf3eb32ca1..40ef457d4d9 100644
--- a/pkg/vm_snapshot_analysis/lib/utils.dart
+++ b/pkg/vm_snapshot_analysis/lib/utils.dart
@@ -13,10 +13,11 @@ import 'package:vm_snapshot_analysis/v8_profile.dart' as v8_profile;
 ProgramInfo loadProgramInfoFromJson(Object json,
     {bool collapseAnonymousClosures = false}) {
   if (v8_profile.Snapshot.isV8HeapSnapshot(json)) {
-    return v8_profile.toProgramInfo(v8_profile.Snapshot.fromJson(json),
+    return v8_profile.toProgramInfo(
+        v8_profile.Snapshot.fromJson(json as Map<String, dynamic>),
         collapseAnonymousClosures: collapseAnonymousClosures);
   } else {
-    return instruction_sizes.loadProgramInfo(json,
+    return instruction_sizes.loadProgramInfo(json as List<dynamic>,
         collapseAnonymousClosures: collapseAnonymousClosures);
   }
 }
@@ -62,7 +63,7 @@ void printHistogram(ProgramInfo info, Histogram histogram,
 
   final visibleRows = [prefix, suffix].expand((l) => l).toList();
   final visibleSize =
-      visibleRows.fold(0, (sum, key) => sum + histogram.buckets[key]);
+      visibleRows.fold<int>(0, (sum, key) => sum + histogram.buckets[key]!);
   final numRestRows = histogram.length - (suffix.length + prefix.length);
   final hiddenRows = Set<String>.from(histogram.bySize)
       .difference(Set<String>.from(visibleRows));
@@ -71,7 +72,7 @@ void printHistogram(ProgramInfo info, Histogram histogram,
 
   if (prefix.isNotEmpty) {
     for (var key in prefix) {
-      final size = histogram.buckets[key];
+      final size = histogram.buckets[key]!;
       table.addRow([
         ...histogram.bucketInfo.namesFromBucket(key),
         size.toString(),
@@ -99,7 +100,7 @@ void printHistogram(ProgramInfo info, Histogram histogram,
       table.addRow([
         ...histogram.bucketInfo.namesFromBucket(key),
         histogram.buckets[key].toString(),
-        formatPercent(histogram.buckets[key], histogram.totalSize),
+        formatPercent(histogram.buckets[key]!, histogram.totalSize),
       ]);
     }
     table.addSeparator(Separator.Line);
diff --git a/pkg/vm_snapshot_analysis/lib/v8_profile.dart b/pkg/vm_snapshot_analysis/lib/v8_profile.dart
index cbbe717a474..7dde86778d3 100644
--- a/pkg/vm_snapshot_analysis/lib/v8_profile.dart
+++ b/pkg/vm_snapshot_analysis/lib/v8_profile.dart
@@ -6,7 +6,7 @@
 /// produced by `--write-v8-snapshot-profile-to` VM flag.
 library vm_snapshot_analysis.v8_profile;
 
-import 'package:meta/meta.dart';
+import 'package:collection/collection.dart';
 
 import 'package:vm_snapshot_analysis/src/dominators.dart' as dominators;
 import 'package:vm_snapshot_analysis/name.dart';
@@ -35,7 +35,7 @@ class Snapshot {
   /// for the given node index.
   final List<int> _edgesStartIndexForNode;
 
-  List<int> _dominators;
+  late final List<int> _dominators = _computeDominators(this);
 
   final List strings;
 
@@ -53,7 +53,6 @@ class Snapshot {
 
   /// Return dominator node for the given node [n].
   Node dominatorOf(Node n) {
-    _dominators ??= _computeDominators(this);
     return nodeAt(_dominators[n.index]);
   }
 
@@ -67,7 +66,7 @@ class Snapshot {
     // Extract meta information first.
     final meta = Meta._fromJson(m['snapshot']['meta']);
 
-    final nodes = m['nodes'];
+    final nodes = (m['nodes'] as List<dynamic>).cast<int>();
 
     // Build an array of starting indexes of edges for each node.
     final edgesStartIndexForNode = <int>[0];
@@ -130,18 +129,18 @@ class Meta {
   final List<String> edgeTypes;
 
   Meta._(
-      {this.nodeTypeIndex,
-      this.nodeNameIndex,
-      this.nodeIdIndex,
-      this.nodeSelfSizeIndex,
-      this.nodeEdgeCountIndex,
-      this.nodeFieldCount,
-      this.edgeTypeIndex,
-      this.edgeNameOrIndexIndex,
-      this.edgeToNodeIndex,
-      this.edgeFieldCount,
-      this.nodeTypes,
-      this.edgeTypes});
+      {required this.nodeTypeIndex,
+      required this.nodeNameIndex,
+      required this.nodeIdIndex,
+      required this.nodeSelfSizeIndex,
+      required this.nodeEdgeCountIndex,
+      required this.nodeFieldCount,
+      required this.edgeTypeIndex,
+      required this.edgeNameOrIndexIndex,
+      required this.edgeToNodeIndex,
+      required this.edgeFieldCount,
+      required this.nodeTypes,
+      required this.edgeTypes});
 
   factory Meta._fromJson(Map<String, dynamic> m) {
     final nodeFields = m['node_fields'];
@@ -171,7 +170,7 @@ class Edge {
   /// Index of this [Edge] within the [snapshot].
   final int index;
 
-  Edge._({this.snapshot, this.index});
+  Edge._({required this.snapshot, required this.index});
 
   String get type => snapshot
       .meta.edgeTypes[snapshot._edges[_offset + snapshot.meta.edgeTypeIndex]];
@@ -212,7 +211,7 @@ class Node {
   /// Index of this [Node] within the [snapshot].
   final int index;
 
-  Node._({this.snapshot, this.index});
+  Node._({required this.snapshot, required this.index});
 
   int get edgeCount =>
       snapshot._nodes[_offset + snapshot.meta.nodeEdgeCountIndex];
@@ -248,10 +247,8 @@ class Node {
   }
 
   /// Returns the target of an outgoing edge with the given name (if any).
-  Node operator [](String edgeName) => this
-      .edges
-      .firstWhere((e) => e.name == edgeName, orElse: () => null)
-      ?.target;
+  Node? operator [](String edgeName) =>
+      this.edges.firstWhereOrNull((e) => e.name == edgeName)?.target;
 
   @override
   bool operator ==(Object other) {
@@ -317,7 +314,7 @@ class _ProgramInfoBuilder {
   /// See [findCommonAncestor] method.
   final Map<int, int> commonAncestorCache = {};
 
-  _ProgramInfoBuilder({this.collapseAnonymousClosures});
+  _ProgramInfoBuilder({required this.collapseAnonymousClosures});
 
   /// Recover [ProgramInfo] structure from the snapshot profile.
   ///
@@ -372,7 +369,7 @@ class _ProgramInfoBuilder {
     return program;
   }
 
-  ProgramInfoNode getInfoNodeFor(Node node) {
+  ProgramInfoNode? getInfoNodeFor(Node node) {
     var info = infoNodeByIndex[node.index];
     if (info == null) {
       info = createInfoNodeFor(node);
@@ -390,7 +387,7 @@ class _ProgramInfoBuilder {
         switch (node.type) {
           case 'Code':
             // Freeze ownership of the Instructions object.
-            final instructions = node['<instructions>'];
+            final instructions = node['<instructions>']!;
             nodesWithFrozenOwner.add(instructions.index);
             ownerOf[instructions.index] =
                 findCommonAncestor(ownerOf[instructions.index], info.id);
@@ -403,7 +400,7 @@ class _ProgramInfoBuilder {
                 if (e.target.type == 'Script') {
                   nodesWithFrozenOwner.add(e.target.index);
                   ownerOf[e.target.index] =
-                      findCommonAncestor(ownerOf[e.target.index], info.id);
+                      findCommonAncestor(ownerOf[e.target.index]!, info.id);
                 }
               }
             }
@@ -414,13 +411,13 @@ class _ProgramInfoBuilder {
     return info;
   }
 
-  ProgramInfoNode createInfoNodeFor(Node node) {
+  ProgramInfoNode? createInfoNodeFor(Node node) {
     switch (node.type) {
       case 'Code':
-        var owner = node['owner_'];
+        final owner = node['owner_']!;
         if (owner.type != 'Type') {
           final ownerNode =
-              owner.type == 'Null' ? program.stubs : getInfoNodeFor(owner);
+              owner.type == 'Null' ? program.stubs : getInfoNodeFor(owner)!;
           if (owner.type == 'Function') {
             // For normal functions we just attribute Code object and all
             // objects dominated by it to the function itself.
@@ -436,29 +433,29 @@ class _ProgramInfoBuilder {
 
       case 'Function':
         if (node.name != '<anonymous signature>') {
-          var owner = node['owner_'];
+          var owner = node['owner_']!;
 
           // Artificial nodes may not have a data_ field.
           var data = node['data_'];
-          if (data?.type == 'ClosureData') {
-            owner = data['parent_function_'];
+          if (data != null && data.type == 'ClosureData') {
+            owner = data['parent_function_']!;
           }
           return makeInfoNode(node.index,
               name: node.name,
-              parent: getInfoNodeFor(owner),
+              parent: getInfoNodeFor(owner)!,
               type: NodeType.functionNode);
         }
         break;
 
       case 'PatchClass':
-        return getInfoNodeFor(node['patched_class_']);
+        return getInfoNodeFor(node['patched_class_']!);
 
       case 'Class':
         // Default to root node. Some builtin classes (void, dynamic) don't have
         // any information about their library written out.
         var ownerNode = program.root;
         if (node['library_'] != null) {
-          ownerNode = getInfoNodeFor(node['library_']) ?? ownerNode;
+          ownerNode = getInfoNodeFor(node['library_']!) ?? ownerNode;
         }
 
         return makeInfoNode(node.index,
@@ -477,20 +474,16 @@ class _ProgramInfoBuilder {
       case 'Field':
         return makeInfoNode(node.index,
             name: node.name,
-            parent: getInfoNodeFor(node['owner_']),
+            parent: getInfoNodeFor(node['owner_']!)!,
             type: NodeType.other);
     }
     return null;
   }
 
-  ProgramInfoNode makeInfoNode(int index,
-      {@required ProgramInfoNode parent,
-      @required String name,
-      @required NodeType type}) {
-    assert(parent != null,
-        'Trying to create node of type ${type} with ${name} and no parent.');
-    assert(name != null);
-
+  ProgramInfoNode makeInfoNode(int? index,
+      {required ProgramInfoNode parent,
+      required String name,
+      required NodeType type}) {
     name = Name(name).scrubbed;
     if (collapseAnonymousClosures) {
       name = Name.collapse(name);
@@ -527,10 +520,10 @@ class _ProgramInfoBuilder {
   }
 
   /// Returns id of a common ancestor between [ProgramInfoNode] with [idA] and
-  /// [idB].
-  int findCommonAncestor(int idA, int idB) {
+  /// [idB]. At least either [idA] or [idB] are expected to be not null.
+  int findCommonAncestor(int? idA, int? idB) {
     if (idA == null) {
-      return idB;
+      return idB!;
     }
     if (idB == null) {
       return idA;
@@ -558,9 +551,8 @@ class _ProgramInfoBuilder {
 
   static List<ProgramInfoNode> pathToRoot(ProgramInfoNode node) {
     final path = <ProgramInfoNode>[];
-    while (node != null) {
-      path.add(node);
-      node = node.parent;
+    for (ProgramInfoNode? n = node; n != null; n = n.parent) {
+      path.add(n);
     }
     return path;
   }
@@ -609,14 +601,15 @@ structure nodes (usually VM internal objects).
 /// The code for dominator tree computation is taken verbatim from the
 /// native compiler (see runtime/vm/compiler/backend/flow_graph.cc).
 List<int> _computeDominators(Snapshot snap) {
-  final predecessors = List<Object>.filled(snap.nodeCount, null);
+  final predecessors = List<Object?>.filled(snap.nodeCount, null);
   void addPred(int n, int p) {
-    if (predecessors[n] == null) {
+    final pred = predecessors[n];
+    if (pred == null) {
       predecessors[n] = p;
-    } else if (predecessors[n] is int) {
-      predecessors[n] = <int>[predecessors[n], p];
+    } else if (pred is int) {
+      predecessors[n] = <int>[pred, p];
     } else {
-      (predecessors[n] as List<int>).add(p);
+      (pred as List<int>).add(p);
     }
   }
 
diff --git a/pkg/vm_snapshot_analysis/pubspec.yaml b/pkg/vm_snapshot_analysis/pubspec.yaml
index 5b75e9164e5..3a37d388fef 100644
--- a/pkg/vm_snapshot_analysis/pubspec.yaml
+++ b/pkg/vm_snapshot_analysis/pubspec.yaml
@@ -5,7 +5,7 @@ version: 0.6.0
 homepage: https://github.com/dart-lang/sdk/tree/master/pkg/vm_snapshot_analysis
 
 environment:
-  sdk: '>=2.8.0 <3.0.0'
+  sdk: '>=2.12.0 <3.0.0'
 
 executables:
   snapshot_analysis: analyse
@@ -13,7 +13,7 @@ executables:
 dependencies:
   args: ^2.0.0
   path: ^1.8.0
-  meta: ^1.3.0
+  collection: ^1.15.0
 
 dev_dependencies:
   pedantic: ^1.11.0
diff --git a/pkg/vm_snapshot_analysis/test/instruction_sizes_test.dart b/pkg/vm_snapshot_analysis/test/instruction_sizes_test.dart
index 5347acc856c..16b25041642 100644
--- a/pkg/vm_snapshot_analysis/test/instruction_sizes_test.dart
+++ b/pkg/vm_snapshot_analysis/test/instruction_sizes_test.dart
@@ -5,6 +5,8 @@
 import 'dart:io';
 
 import 'package:test/test.dart';
+import 'package:collection/collection.dart';
+
 import 'package:vm_snapshot_analysis/instruction_sizes.dart'
     as instruction_sizes;
 import 'package:vm_snapshot_analysis/program_info.dart';
@@ -242,7 +244,7 @@ void main() async {
     test('basic-parsing', () async {
       await withSymbolSizes(testSource, (sizesJson) async {
         final json = await loadJson(File(sizesJson));
-        final symbols = instruction_sizes.fromJson(json);
+        final symbols = instruction_sizes.fromJson(json as List<dynamic>);
         expect(symbols, isNotNull,
             reason: 'Sizes file was successfully parsed');
         expect(symbols.length, greaterThan(0),
@@ -254,7 +256,7 @@ void main() async {
         final symbolScrubbedNames = <String, Map<String, Set<String>>>{};
 
         Set<String> getSetOfNames(Map<String, Map<String, Set<String>>> map,
-            String libraryUri, String className) {
+            String? libraryUri, String? className) {
           return map
               .putIfAbsent(libraryUri ?? '', () => {})
               .putIfAbsent(className ?? '', () => {});
@@ -280,10 +282,12 @@ void main() async {
         expect(inputDartSymbolNames, isNotNull,
             reason: 'Symbols from input.dart are included into sizes output');
 
+        inputDartSymbolNames!; // Checked above. Promote the variable type.
+
         expect(inputDartSymbolNames[''], isNotNull,
             reason: 'Should include top-level members from input.dart');
         expect(inputDartSymbolNames[''], contains('makeSomeClosures'));
-        final closures = inputDartSymbolNames[''].where(
+        final closures = inputDartSymbolNames['']!.where(
             (name) => name.startsWith('makeSomeClosures.<anonymous closure'));
         expect(closures.length, 3,
             reason: 'There are three closures inside makeSomeClosure');
@@ -311,7 +315,7 @@ void main() async {
         expect(inputDartSymbolNames['D'], contains('[tear-off] tornOff'));
 
         // Check that output does not contain '[unknown stub]'
-        expect(symbolRawNames[''][''], isNot(contains('[unknown stub]')),
+        expect(symbolRawNames['']![''], isNot(contains('[unknown stub]')),
             reason: 'All stubs must be named');
       });
     });
@@ -324,19 +328,18 @@ void main() async {
         expect(info.root.children, contains('dart:typed_data'));
         expect(info.root.children, contains('package:input'));
 
-        final inputLib = info.root.children['package:input']
-            .children['package:input/input.dart'];
-        expect(inputLib, isNotNull);
+        final inputLib = info.root.children['package:input']!
+            .children['package:input/input.dart']!;
         expect(inputLib.children, contains('')); // Top-level class.
         expect(inputLib.children, contains('A'));
         expect(inputLib.children, contains('B'));
         expect(inputLib.children, contains('C'));
         expect(inputLib.children, contains('D'));
 
-        final topLevel = inputLib.children[''];
+        final topLevel = inputLib.children['']!;
         expect(topLevel.children, contains('makeSomeClosures'));
         expect(
-            topLevel.children['makeSomeClosures'].children.length, equals(3));
+            topLevel.children['makeSomeClosures']!.children.length, equals(3));
 
         for (var name in [
           '[tear-off] tornOff',
@@ -344,8 +347,8 @@ void main() async {
           'Allocate A',
           '[tear-off-extractor] get:tornOff'
         ]) {
-          expect(inputLib.children['A'].children, contains(name));
-          expect(inputLib.children['A'].children[name].children, isEmpty);
+          expect(inputLib.children['A']!.children, contains(name));
+          expect(inputLib.children['A']!.children[name]!.children, isEmpty);
         }
 
         for (var name in [
@@ -354,13 +357,13 @@ void main() async {
           'Allocate B',
           '[tear-off-extractor] get:tornOff'
         ]) {
-          expect(inputLib.children['B'].children, contains(name));
-          expect(inputLib.children['B'].children[name].children, isEmpty);
+          expect(inputLib.children['B']!.children, contains(name));
+          expect(inputLib.children['B']!.children[name]!.children, isEmpty);
         }
 
         for (var name in ['tornOff{body}', 'tornOff', '[tear-off] tornOff']) {
-          expect(inputLib.children['C'].children, contains(name));
-          expect(inputLib.children['C'].children[name].children, isEmpty);
+          expect(inputLib.children['C']!.children, contains(name));
+          expect(inputLib.children['C']!.children[name]!.children, isEmpty);
         }
 
         for (var name in [
@@ -369,8 +372,8 @@ void main() async {
           'tornOff',
           '[tear-off] tornOff'
         ]) {
-          expect(inputLib.children['D'].children, contains(name));
-          expect(inputLib.children['D'].children[name].children, isEmpty);
+          expect(inputLib.children['D']!.children, contains(name));
+          expect(inputLib.children['D']!.children[name]!.children, isEmpty);
         }
       });
     });
@@ -435,6 +438,64 @@ void main() async {
       });
     });
 
+    test('histograms-filter', () async {
+      await withSymbolSizes(testSource, (sizesJson) async {
+        final json = await loadJson(File(sizesJson));
+        final info = loadProgramInfoFromJson(json);
+
+        {
+          final h = computeHistogram(info, HistogramType.bySymbol,
+              filter: 'A.tornOff');
+          expect(
+              h.buckets,
+              contains(h.bucketFor('package:input', 'package:input/input.dart',
+                  'A', 'tornOff')));
+          expect(
+              h.buckets,
+              isNot(contains(h.bucketFor('package:input',
+                  'package:input/input.dart', 'B', 'tornOff'))));
+        }
+
+        {
+          final h = computeHistogram(info, HistogramType.bySymbol,
+              filter: '::A*tornOff');
+          expect(
+              h.buckets,
+              contains(h.bucketFor('package:input', 'package:input/input.dart',
+                  'A', 'tornOff')));
+          expect(
+              h.buckets,
+              isNot(contains(h.bucketFor('package:input',
+                  'package:input/input.dart', 'B', 'tornOff'))));
+        }
+
+        {
+          final h = computeHistogram(info, HistogramType.bySymbol,
+              filter: 'input.dart*tornOff');
+          expect(
+              h.buckets,
+              contains(h.bucketFor('package:input', 'package:input/input.dart',
+                  'A', 'tornOff')));
+          expect(
+              h.buckets,
+              contains(h.bucketFor('package:input', 'package:input/input.dart',
+                  'B', 'tornOff')));
+        }
+
+        {
+          final h =
+              computeHistogram(info, HistogramType.byPackage, filter: 'A');
+          expect(
+              h.buckets,
+              contains(h.bucketFor(
+                  'package:input',
+                  'package:input/does-not-matter.dart',
+                  'does-not-matter',
+                  'does-not-matter')));
+        }
+      });
+    });
+
     test('diff', () async {
       await withSymbolSizes(testSource, (sizesJson) async {
         await withSymbolSizes(testSourceModified, (modifiedSizesJson) async {
@@ -534,18 +595,17 @@ void main() async {
         expect(info.root.children, contains('dart:typed_data'));
         expect(info.root.children, contains('package:input'));
 
-        final inputLib = info.root.children['package:input']
-            .children['package:input/input.dart'];
-        expect(inputLib, isNotNull);
+        final inputLib = info.root.children['package:input']!
+            .children['package:input/input.dart']!;
         expect(inputLib.children, contains('::')); // Top-level class.
         expect(inputLib.children, contains('A'));
         expect(inputLib.children, contains('B'));
         expect(inputLib.children, contains('C'));
 
-        final topLevel = inputLib.children['::'];
+        final topLevel = inputLib.children['::']!;
         expect(topLevel.children, contains('makeSomeClosures'));
         expect(
-            topLevel.children['makeSomeClosures'].children.values
+            topLevel.children['makeSomeClosures']!.children.values
                 .where((child) => child.type == NodeType.functionNode)
                 .length,
             equals(3));
@@ -555,9 +615,9 @@ void main() async {
           'Allocate A',
           '[tear-off-extractor] get:tornOff'
         ]) {
-          expect(inputLib.children['A'].children, contains(name));
+          expect(inputLib.children['A']!.children, contains(name));
         }
-        expect(inputLib.children['A'].children['tornOff'].children,
+        expect(inputLib.children['A']!.children['tornOff']!.children,
             contains('[tear-off] tornOff'));
 
         for (var name in [
@@ -565,35 +625,35 @@ void main() async {
           'Allocate B',
           '[tear-off-extractor] get:tornOff'
         ]) {
-          expect(inputLib.children['B'].children, contains(name));
+          expect(inputLib.children['B']!.children, contains(name));
         }
-        expect(inputLib.children['B'].children['tornOff'].children,
+        expect(inputLib.children['B']!.children['tornOff']!.children,
             contains('[tear-off] tornOff'));
 
-        final classC = inputLib.children['C'];
+        final classC = inputLib.children['C']!;
         expect(classC.children, contains('tornOff'));
         for (var name in ['tornOff{body}', '[tear-off] tornOff']) {
-          expect(classC.children['tornOff'].children, contains(name));
+          expect(classC.children['tornOff']!.children, contains(name));
         }
 
         // Verify that [ProgramInfoNode] owns its corresponding snapshot [Node].
-        final classesOwnedByC = info.snapshotInfo.snapshot.nodes
-            .where((n) => info.snapshotInfo.ownerOf(n) == classC)
+        final classesOwnedByC = info.snapshotInfo!.snapshot.nodes
+            .where((n) => info.snapshotInfo!.ownerOf(n) == classC)
             .where((n) => n.type == 'Class')
             .map((n) => n.name);
         expect(classesOwnedByC, equals(['C']));
 
-        final classD = inputLib.children['D'];
+        final classD = inputLib.children['D']!;
         expect(classD.children, contains('tornOff'));
         for (var name in ['tornOff{body}', '[tear-off] tornOff']) {
-          expect(classD.children['tornOff'].children, contains(name));
+          expect(classD.children['tornOff']!.children, contains(name));
         }
-        expect(classD.children['tornOff'].children['tornOff{body}'].children,
+        expect(classD.children['tornOff']!.children['tornOff{body}']!.children,
             contains('tornOff{body depth 2}'));
 
         // Verify that [ProgramInfoNode] owns its corresponding snapshot [Node].
-        final classesOwnedByD = info.snapshotInfo.snapshot.nodes
-            .where((n) => info.snapshotInfo.ownerOf(n) == classD)
+        final classesOwnedByD = info.snapshotInfo!.snapshot.nodes
+            .where((n) => info.snapshotInfo!.ownerOf(n) == classD)
             .where((n) => n.type == 'Class')
             .map((n) => n.name);
         expect(classesOwnedByD, equals(['D']));
@@ -616,20 +676,20 @@ void main() async {
             '::',
             'makeSomeClosures'
           ]);
-          final codeNode = fromProfile.snapshotInfo.snapshot.nodes.firstWhere(
+          final codeNode = fromProfile.snapshotInfo!.snapshot.nodes.firstWhere(
               (n) =>
                   n.type == 'Code' &&
-                  fromProfile.snapshotInfo.ownerOf(n) == functionNode &&
+                  fromProfile.snapshotInfo!.ownerOf(n) == functionNode &&
                   n.name.contains('makeSomeClosures'));
           expect(codeNode['<instructions>'], isNotNull);
-          final instructionsSize = codeNode['<instructions>'].selfSize;
+          final instructionsSize = codeNode['<instructions>']!.selfSize;
           final symbolSize = fromSymbolSizes.lookup([
             'package:input',
             'package:input/input.dart',
             '',
             'makeSomeClosures'
-          ]).size;
-          expect(instructionsSize - symbolSize, equals(0));
+          ])!.size;
+          expect(instructionsSize - symbolSize!, equals(0));
         });
       });
     });
@@ -786,9 +846,10 @@ void main() async {
 
         String nameOf(Map<String, dynamic> node) => node['n'];
 
-        Map<String, dynamic> findChild(Map<String, dynamic> node, String name) {
+        Map<String, dynamic>? findChild(
+            Map<String, dynamic> node, String name) {
           return childrenOf(node)
-              .firstWhere((child) => nameOf(child) == name, orElse: () => null);
+              .firstWhereOrNull((child) => nameOf(child) == name);
         }
 
         Set<String> childrenNames(Map<String, dynamic> node) {
@@ -802,7 +863,7 @@ void main() async {
           // for some reason.
           expect(findChild(treemap, 'package:input/input.dart'), isNotNull);
         } else {
-          expect(childrenNames(findChild(treemap, 'package:input')),
+          expect(childrenNames(findChild(treemap, 'package:input')!),
               equals({'main.dart', 'input.dart'}));
         }
       });
@@ -813,7 +874,7 @@ void main() async {
         // Note: computing dominators also verifies that we don't have
         // unreachable nodes in the snapshot.
         final infoJson = await loadJson(File(profileJson));
-        final snapshot = Snapshot.fromJson(infoJson);
+        final snapshot = Snapshot.fromJson(infoJson as Map<String, dynamic>);
         for (var n in snapshot.nodes.skip(1)) {
           expect(snapshot.dominatorOf(n), isNotNull);
         }
@@ -839,7 +900,7 @@ Future withV8Profile(
 // simply ignore entry point library (main.dart).
 // Additionally this function removes all nodes with the size below
 // the given threshold.
-Map<String, dynamic> diffToJson(ProgramInfo diff,
+Map<String, dynamic>? diffToJson(ProgramInfo diff,
     {bool keepOnlyInputPackage = false}) {
   final diffJson = diff.toJson();
   diffJson.removeWhere((key, _) =>
@@ -847,7 +908,7 @@ Map<String, dynamic> diffToJson(ProgramInfo diff,
 
   // Rebuild the diff JSON discarding all nodes with size below threshold.
   const smallChangeThreshold = 16;
-  Map<String, dynamic> discardSmallChanges(Map<String, dynamic> map) {
+  Map<String, dynamic>? discardSmallChanges(Map<String, dynamic> map) {
     final result = <String, dynamic>{};
 
     // First recursively process all children (skipping #type and #size keys).
diff --git a/pkg/vm_snapshot_analysis/test/precompiler_trace_test.dart b/pkg/vm_snapshot_analysis/test/precompiler_trace_test.dart
index 239217127e6..f00e9778e52 100644
--- a/pkg/vm_snapshot_analysis/test/precompiler_trace_test.dart
+++ b/pkg/vm_snapshot_analysis/test/precompiler_trace_test.dart
@@ -75,7 +75,7 @@ void main() async {
         callGraph.computeDominators();
 
         final main = callGraph.program
-            .lookup(['package:input', 'package:input/input.dart', '', 'main']);
+            .lookup(['package:input', 'package:input/input.dart', '', 'main'])!;
         final mainNode = callGraph.lookup(main);
 
         final retainedClasses = mainNode.dominated
diff --git a/pkg/vm_snapshot_analysis/test/utils.dart b/pkg/vm_snapshot_analysis/test/utils.dart
index 830ca06492a..1163ae7f2bc 100644
--- a/pkg/vm_snapshot_analysis/test/utils.dart
+++ b/pkg/vm_snapshot_analysis/test/utils.dart
@@ -24,7 +24,7 @@ class AotSnapshot {
   final String outputBinary;
   final String sizesJson;
 
-  AotSnapshot({this.outputBinary, this.sizesJson});
+  AotSnapshot({required this.outputBinary, required this.sizesJson});
 }
 
 Future withFlag(
@@ -33,7 +33,7 @@ Future withFlag(
 }
 
 Future withFlagImpl(
-    Map<String, String> source, String flag, Future Function(AotSnapshot) f) {
+    Map<String, String> source, String? flag, Future Function(AotSnapshot) f) {
   return withTempDir((dir) async {
     final snapshot = AotSnapshot(
       outputBinary: path.join(dir, 'output.exe'),
@@ -90,7 +90,8 @@ stderr: ${result.stderr}
   });
 }
 
-const keepTempKey = 'KEEP_TEMPORARY_DIRECTORIES';
+late final shouldKeepTemporaryDirectories =
+    Platform.environment['KEEP_TEMPORARY_DIRECTORIES']?.isNotEmpty == true;
 
 Future withTempDir(Future Function(String dir) f) async {
   final tempDir =
@@ -98,17 +99,16 @@ Future withTempDir(Future Function(String dir) f) async {
   try {
     await f(tempDir.path);
   } finally {
-    if (!Platform.environment.containsKey(keepTempKey) ||
-        Platform.environment[keepTempKey].isEmpty) {
+    if (shouldKeepTemporaryDirectories) {
       tempDir.deleteSync(recursive: true);
     }
   }
 }
 
 Future<Object> loadJson(File input) async {
-  return await input
+  return (await input
       .openRead()
       .transform(utf8.decoder)
       .transform(json.decoder)
-      .first;
+      .first)!;
 }