Roll Dart SDK from 1d9c734bd5c0 to dfef9e3dc99b (1 revision) (#33386)

diff --git a/DEPS b/DEPS
index 270875e..14b91e8 100644
--- a/DEPS
+++ b/DEPS
@@ -45,7 +45,7 @@
   # Dart is: https://github.com/dart-lang/sdk/blob/main/DEPS.
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': '1d9c734bd5c01e65f44f0e864d9584b5cc62192f',
+  'dart_revision': 'dfef9e3dc99b8f86a151257eb7f264ab02171602',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py