Roll Dart SDK from b1afd0f to 307a0e7 (1 revision) (#29878)

Author: skia-flutter-autoroll

DEPS

@@ -39,7 +39,7 @@ vars = {
   # Dart is: https://github.com/dart-lang/sdk/blob/main/DEPS.
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': 'b1afd0fae784e0d3c4f86bf7e028522bbbe8c086',
+  'dart_revision': '307a0e73531736f121b40211b857eb2fb160158c',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py