Roll Dart SDK from 2091ff4 to 7b6056f (1 revision) (#30259)

https://dart.googlesource.com/sdk.git/+log/2091ff49c513..7b6056f9db7f

2021-12-09 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.16.0-94.0.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,jsimmons@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

@@ -39,7 +39,7 @@ 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': '2091ff49c513576c6a01fde8e525a9aba3fe3bb6',
+  'dart_revision': '7b6056f9db7f05bf0e182796b7fec8edbe9c8231',
 
   # 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: db57f9b95c92fb4c77969202ea22d338
+Signature: fcaaa2659f4d5ddf584020fe4fb16563
 
 UNUSED LICENSES: