Roll Dart SDK from 7c061d8c9dc0 to 4d084f5b8f91 (1 revision) (flutter/engine#41686)

https://dart.googlesource.com/sdk.git/+log/7c061d8c9dc0..4d084f5b8f91

2023-05-02 dart-internal-merge@dart-ci-internal.iam.gserviceaccount.com Version 3.1.0-67.0.dev

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/dart-sdk-flutter-engine
Please CC aam@google.com,dart-vm-team@google.com,jimgraham@google.com,rmistry@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in Flutter Engine: https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

DEPS

@@ -53,7 +53,7 @@ vars = {
   # Dart is: https://github.com/dart-lang/sdk/blob/main/DEPS
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': '7c061d8c9dc0cc11245f1eed26f15bae37e11d0b',
+  'dart_revision': '4d084f5b8f91bfdd1c520ba6a3abf6e176c728f8',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py
@@ -336,7 +336,7 @@ deps = {
    Var('dart_git') + '/args.git@5ac2ba1d93f037c7aee2975703bf071f88597a76',
 
   'src/third_party/dart/third_party/pkg/async':
-   Var('dart_git') + '/async.git@ce650b0ce8fa95fc13d4744a293f3e9b00266bee',
+   Var('dart_git') + '/async.git@b9ed21948754001e31e209612b6ef8a5b2ad8e9f',
 
   'src/third_party/dart/third_party/pkg/bazel_worker':
    Var('dart_git') + '/bazel_worker.git@d5f88375b41def124aa65be1d4da8a2c9e82e076',