Roll Dart SDK from fabaeef00dfb to b6de2d42e58d (2 revisions) (#41401)

https://dart.googlesource.com/sdk.git/+log/fabaeef00dfb..b6de2d42e58d

2023-04-21 dart-internal-merge@dart-ci-internal.iam.gserviceaccount.com Version 3.1.0-30.0.dev
2023-04-21 dart-internal-merge@dart-ci-internal.iam.gserviceaccount.com Version 3.1.0-29.0.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,chinmaygarde@google.com,dart-vm-team@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

Author: skia-flutter-autoroll

DEPS

@@ -47,7 +47,7 @@ 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': 'fabaeef00dfb49ecb107fbad9b2cd941acc933ac',
+  'dart_revision': 'b6de2d42e58d249bb52a0b52fcac81d9925a2bcb',
 
   # 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: e95e1e091efbcda23a1610b2f718f7a4
+Signature: 302533c6e10c1b1ac9bca53aac4d636f
 
 ====================================================================================================
 LIBRARY: angle