Temporary revert of Dart SDK rolls made since 2019/01/08 (#7437)

DEPS

@@ -31,7 +31,7 @@ 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': '651d19cdaa25d020b8f7c193c907644284029130',
+  'dart_revision': '2cb346bd0cce075a5b7988cedb678e822a1d50f4',
 
   # 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

-Signature: 82c34939fde067743b8863d6ae94c7de
+Signature: 1151287898856aac5ec88018bdb049ab
 
 UNUSED LICENSES: