Roll Dart SDK from b776411 to fee865e (1 revision) (flutter#24839)

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': 'b77641194368f747c74cc935ce1b550b00ec9b2f',
+  'dart_revision': 'fee865ec64048a42d160b0567da77738be7341b5',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py