Roll Dart SDK from b5ff349 to a45eaf6 (1 revision) (#25837)

Author: skia-flutter-autoroll

DEPS

@@ -35,7 +35,7 @@ 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': 'b5ff349bffc848262ce67960461c1eecbb89e72f',
+  'dart_revision': 'a45eaf6402c3941823703502094199ed0bb01a1b',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py