Roll Dart SDK from 4b9aa2bd7ecb to 7e5fe50b244c (4 revisions) (flutter#19080)

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': '4b9aa2bd7ecb0c868d9062e68162afae489fc31d',
+  'dart_revision': '7e5fe50b244cd94851551ef04dea6d5d5261002d',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py