diff --git a/tools/bots/update_flakiness.dart b/tools/bots/update_flakiness.dart
index 71bf4023b6b..2f4f680a6d9 100755
--- a/tools/bots/update_flakiness.dart
+++ b/tools/bots/update_flakiness.dart
@@ -12,105 +12,90 @@ import 'package:args/args.dart';
 
 import 'package:test_runner/bot_results.dart';
 
-main(List<String> args) async {
-  final parser = new ArgParser();
+void main(List<String> args) async {
+  final parser = ArgParser();
   parser.addFlag('help', help: 'Show the program usage.', negatable: false);
-  parser.addOption('input', abbr: 'i', help: "Input flakiness file.");
-  parser.addOption('output', abbr: 'o', help: "Output flakiness file.");
-  parser.addOption('build-id', help: "Logdog ID of this buildbot run");
-  parser.addOption('commit', help: "Commit hash of this buildbot run");
+  parser.addOption('input', abbr: 'i', help: 'Input flakiness file.');
+  parser.addOption('output', abbr: 'o', help: 'Output flakiness file.');
+  parser.addOption('build-id', help: 'Logdog ID of this buildbot run');
+  parser.addOption('commit', help: 'Commit hash of this buildbot run');
+  parser.addFlag('no-forgive', help: 'Don\'t remove any flaky records');
 
   final options = parser.parse(args);
-  if (options["help"]) {
-    print("""
+  if (options['help']) {
+    print('''
 Usage: update_flakiness.dart [OPTION]... [RESULT-FILE]...
 Update the flakiness data with a set of fresh results.
 
 The options are as follows:
 
-${parser.usage}""");
+${parser.usage}''');
     return;
   }
   final parameters = options.rest;
 
   // Load the existing flakiness data, if any.
-  final data = options["input"] != null
-      ? await loadResultsMap(options["input"])
+  final data = options['input'] != null
+      ? await loadResultsMap(options['input'])
       : <String, Map<String, dynamic>>{};
 
   // Incrementally update the flakiness data with each observed result.
   for (final path in parameters) {
     final results = await loadResults(path);
     for (final resultObject in results) {
-      final String configuration = resultObject["configuration"];
-      final String name = resultObject["name"];
-      final String result = resultObject["result"];
-      final key = "$configuration:$name";
-      newMap() => <String, dynamic>{};
-      final Map<String, dynamic> testData = data.putIfAbsent(key, newMap);
-      testData["configuration"] = configuration;
-      testData["name"] = name;
-      testData["expected"] = resultObject["expected"];
-      final outcomes = testData.putIfAbsent("outcomes", () => []);
+      final String configuration = resultObject['configuration'];
+      final String name = resultObject['name'];
+      final String result = resultObject['result'];
+      final key = '$configuration:$name';
+      Map<String, dynamic> newMap() => {};
+      final testData = data.putIfAbsent(key, newMap);
+      testData['configuration'] = configuration;
+      testData['name'] = name;
+      testData['expected'] = resultObject['expected'];
+      final outcomes = testData.putIfAbsent('outcomes', () => []);
       final time = DateTime.now().toIso8601String();
       if (!outcomes.contains(result)) {
         outcomes
           ..add(result)
           ..sort();
-        testData["last_new_result_seen"] = time;
+        testData['last_new_result_seen'] = time;
       }
-      if (testData["current"] == result) {
-        testData["current_counter"]++;
+      if (testData['current'] == result) {
+        testData['current_counter']++;
       } else {
-        testData["current"] = result;
-        testData["current_counter"] = 1;
+        testData['current'] = result;
+        testData['current_counter'] = 1;
       }
-      final occurrences = testData.putIfAbsent("occurrences", newMap);
+      final occurrences = testData.putIfAbsent('occurrences', newMap);
       occurrences.putIfAbsent(result, () => 0);
       occurrences[result]++;
-      final firstSeen = testData.putIfAbsent("first_seen", newMap);
+      final firstSeen = testData.putIfAbsent('first_seen', newMap);
       firstSeen.putIfAbsent(result, () => time);
-      final lastSeen = testData.putIfAbsent("last_seen", newMap);
+      final lastSeen = testData.putIfAbsent('last_seen', newMap);
       lastSeen[result] = time;
-      final matches = testData.putIfAbsent("matches", newMap);
-      // TODO: Temporarily fill in the matches field for all other outcomes.
-      // Remove this when all the builders have run at least once.
-      for (final outcome in occurrences.keys) {
-        matches[outcome] = resultObject["expected"] == "Fail"
-            ? ["Fail", "CompileTimeError", "RuntimeError"].contains(outcome)
-            : resultObject["expected"] == outcome;
-      }
-      matches[result] = resultObject["matches"];
+      final matches = testData.putIfAbsent('matches', newMap);
+      matches[result] = resultObject['matches'];
 
-      if (options["build-id"] != null) {
-        final buildIds = testData.putIfAbsent("build_ids", newMap);
-        buildIds[result] = options["build-id"];
+      if (options['build-id'] != null) {
+        final buildIds = testData.putIfAbsent('build_ids', newMap);
+        buildIds[result] = options['build-id'];
       }
-      if (options["commit"] != null) {
-        final commits = testData.putIfAbsent("commits", newMap);
-        commits[result] = options["commit"];
+      if (options['commit'] != null) {
+        final commits = testData.putIfAbsent('commits', newMap);
+        commits[result] = options['commit'];
       }
     }
   }
 
-  // Write out the new flakiness data, containing all the tests known to have
-  // multiple outcomes.
-  final sink = options["output"] != null
-      ? new File(options["output"]).openWrite()
-      : stdout;
-  final keys = new List<String>.from(data.keys)..sort();
+  // Write out the new flakiness data.
+  final sink =
+      options['output'] != null ? File(options['output']).openWrite() : stdout;
+  final keys = data.keys.toList()..sort();
   for (final key in keys) {
     final testData = data[key];
-    if (testData["outcomes"].length < 2) continue;
-    // TODO: Temporarily discard entries for old tests that don't run. Remove
-    // this when all the builders have run at least once.
-    if (!testData.containsKey("matches")) {
-      continue;
-    }
-    // Forgive tests that have become deterministic again. If they flake less
-    // than once in a 100 (p<1%), then if they flake again, the probability of
-    // them getting past 5 runs of deflaking is 1%^5 = 0.00000001%.
-    if (100 <= testData["current_counter"]) {
+    if (testData['outcomes'].length < 2) continue;
+    // Forgive tests that have been stable for 100 builds.
+    if (!options['no-forgive'] && testData['current_counter'] >= 100) {
       continue;
     }
     sink.writeln(jsonEncode(testData));