Roll Dart SDK from 2b84af1 to abecc4b (1 revision) (#28259)

Author: skia-flutter-autoroll

DEPS

@@ -39,7 +39,7 @@ 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': '2b84af1e5f1a295b9c94d070204e1965ea377aee',
+  'dart_revision': 'abecc4bc45215cf121b38feee6f118fe428bac78',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py