Roll Dart SDK from 1697706 to ab50477 (5 revisions) (#30690)

https://dart.googlesource.com/sdk.git/+log/1697706df708..ab5047720a9e

2021-12-28 [email protected] Version 2.16.0-139.0.dev
2021-12-28 [email protected] Version 2.16.0-138.0.dev
2021-12-28 [email protected] Version 2.16.0-137.0.dev
2021-12-27 [email protected] Version 2.16.0-136.0.dev
2021-12-24 [email protected] Version 2.16.0-135.0.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 [email protected],[email protected] 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': '1697706df708daaefe02450726f80a69990d10d8',
+  'dart_revision': 'ab5047720a9ea7dd58c638fd8cfbc7f548f30f54',
 
   # 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: f2ec71732217d338f5d9e4b65e847175
+Signature: 79b0c354265bcb11af475cd806235eed
 
 UNUSED LICENSES: