Roll Dart SDK from 0546ef689975 to 4b6978f8afef (1 revision) (#25768)

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': '0546ef6899755508e538916245ff069e5266d4b5',
+  'dart_revision': '4b6978f8afefb3fd5aaa60d8bf5d144fba47be71',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py

ci/licenses_golden/licenses_third_party

-Signature: 744c8e6c894cc0bdd43d222735a22afa
+Signature: 68d3e5e30e9523d7b4849fdc40cb6e22
 
 UNUSED LICENSES: