Roll Dart SDK from bf20abb to 7bbace2 (1 revision) (flutter#22515)

https://dart.googlesource.com/sdk.git/+log/bf20abbb8e22..7bbace20d14f

2020-11-13 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.12.0-41.0.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 on the revert to ensure that a human
is aware of the problem.

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/master/autoroll/README.md

Author: skia-flutter-autoroll

DEPS

@@ -34,7 +34,7 @@ vars = {
   # Dart is: https://github.com/dart-lang/sdk/blob/master/DEPS.
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': 'bf20abbb8e22e0cec1eff2b0db5f1d35eea3a9d0',
+  'dart_revision': '7bbace20d14f05890f20571e832bd18b97f039d7',
 
   # 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: 3197ae288d72d172297463536a2fa97b
+Signature: f6a46168a0e2927475150466ee5cfa94
 
 UNUSED LICENSES: