Roll src/third_party/dart 2bc0f49c00..9b23c483ba (1 commits)

dart-lang/sdk@9b23c483ba Revert "Make package:expect NNBD agnostic"

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': '2bc0f49c00a9537121154d858604934ec04477b6',
+  'dart_revision': '9b23c483ba61ff1c7a15cbb658c4ff4babc3046e',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py