Roll Dart SDK from 6eab35f49cbb to 2a5f37d25453 (1 revision) (#20917)

https://dart.googlesource.com/sdk.git/+log/6eab35f49cbb..2a5f37d25453

2020-09-01 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.10.0-80.0.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

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': '6eab35f49cbb7740f54162e1e57c864b3b0ea06b',
+  'dart_revision': '2a5f37d2545304b1065bf9a6e6cc42f5e88c772a',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py