[vm] Enable nnbd experiment when building the SDK with --nnbd

This is necessary as of https://dart-review.googlesource.com/c/sdk/+/127961
to use the experiment flag in the VM.

Tested: Late modifier tests that had stopped building now pass again.

Change-Id: I49a5f1e99f40c6e8d785b28a333b44e6fac67eca
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127984
Commit-Queue: Liam Appelbe <liama@google.com>
Reviewed-by: Régis Crelier <regis@google.com>

runtime/bin/BUILD.gn

@@ -552,9 +552,7 @@ gen_snapshot_action("generate_snapshot_bin") {
   ]
   args = []
   if (use_nnbd) {
-    # TODO(sigmund): reenable this flag once the CFE can build targets without
-    # issues.
-    # args += [ "--enable-experiment=non-nullable" ]
+    args += [ "--enable-experiment=non-nullable" ]
   }
   args += [
     "--deterministic",

runtime/vm/BUILD.gn

@@ -153,9 +153,7 @@ template("gen_vm_platform") {
       "-Ddart.isVM=true",
     ]
     if (use_nnbd) {
-      # TODO(sigmund): reenable this flag once the CFE can build targets without
-      # issues.
-      # args += [ "--enable-experiment=non-nullable" ]
+      args += [ "--enable-experiment=non-nullable" ]
     }
     if (defined(invoker.exclude_source) && invoker.exclude_source) {
       args += [ "--exclude-source" ]

sdk_nnbd/bin/dartdevc

@@ -45,4 +45,4 @@ DART_ROOT="$(cd "${SDK_DIR}/.." ; pwd -P)"
 
 DEV_COMPILER="$DART_ROOT/pkg/dev_compiler/bin/dartdevc.dart"
 
-exec "$DART" "--packages=$DART_ROOT/.packages" "${EXTRA_VM_OPTIONS[@]}" "$DEV_COMPILER" "$SDK_ARG" "$@"
+exec "$DART" "--packages=$DART_ROOT/.packages" --enable_experiment=non-nullable "${EXTRA_VM_OPTIONS[@]}" "$DEV_COMPILER" "$SDK_ARG" "$@"

sdk_nnbd/bin/dartdevc_sdk

@@ -35,4 +35,4 @@ if [[ $DART_VM_OPTIONS ]]; then
   EXTRA_VM_OPTIONS+=("${OPTIONS[@]}")
 fi
 
-exec "$DART" "${EXTRA_VM_OPTIONS[@]}" "$SNAPSHOT" "$@"
+exec "$DART" --enable_experiment=non-nullable "${EXTRA_VM_OPTIONS[@]}" "$SNAPSHOT" "$@"

utils/application_snapshot.gni

@@ -4,6 +4,7 @@
 
 import("../build/dart/dart_action.gni")
 import("../runtime/runtime_args.gni")
+import("../sdk_args.gni")
 
 _dart_root = get_path_info("..", "abspath")
 
@@ -146,6 +147,10 @@ template("_application_snapshot") {
                 "--snapshot-depfile=$abs_depfile",
               ] + snapshot_vm_args
 
+    if (use_nnbd) {
+      vm_args += [ "--enable-experiment=non-nullable" ]
+    }
+
     if (dart_snapshot_kind == "kernel") {
       vm_args += [ "--snapshot-kind=kernel" ]
       assert(training_args != "", "Ignoring unused argument")