Roll Dart SDK from 5ea7e4d to 6a805f4 (1 revision) (flutter#22518)

https://dart.googlesource.com/sdk.git/+log/5ea7e4d39f43..6a805f4dbcf4

2020-11-14 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.12.0-43.0.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': '5ea7e4d39f43bafdebaf1010eafe96cd292da4d1',
+  'dart_revision': '6a805f4dbcf4be71f609d187973f4d6b6e1d14c4',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py