Roll Dart SDK from b7fe6e0c274c to 3a9145a57432 (1 revision) (#42668)

https://dart.googlesource.com/sdk.git/+log/b7fe6e0c274c..3a9145a57432

2023-06-08 dart-internal-merge@dart-ci-internal.iam.gserviceaccount.com Version 3.1.0-186.0.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 dart-vm-team@google.com,jacksongardner@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

Author: skia-flutter-autoroll

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': 'b7fe6e0c274cb512e811981bfc6de0edc7150b4e',
+  'dart_revision': '3a9145a5743209e5aa4e25adc219a99eed3c59bc',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py

ci/licenses_golden/licenses_third_party

@@ -1,4 +1,4 @@
-Signature: 713393d44593bbfa5cd6e40cfe916605
+Signature: 9f88115b7eed4568e0c5f9fa5978616b
 
 ====================================================================================================
 LIBRARY: angle