Roll src/third_party/dart 05103dfe5a0e..a8251f820b09 (4 commits) (#17526)

diff --git a/DEPS b/DEPS
index d26362f..7d6cc5d 100644
--- a/DEPS
+++ b/DEPS
@@ -34,7 +34,7 @@
   # 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': '05103dfe5a0e2f354f33c96da7bbf13dc79c3915',
+  'dart_revision': 'a8251f820b0975f07f9868c8468d0b32805857e2',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py