Roll Dart SDK from 871f0ee31eb0 to f91547d6dd45 (1 revision) (flutter#19350)

Author: skia-flutter-autoroll

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': '871f0ee31eb088911286907b458ade30a529e01e',
+  'dart_revision': 'f91547d6dd45d09e787d2f9d0d5656e3d3c75af1',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py