Revert "Roll Dart SDK from 4851720 to 3ed1fc1 (1 revision) (flutter#37920)"

This reverts commit 08995ff.

Author: zanderso

DEPS

@@ -48,7 +48,7 @@ vars = {
   # 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': '3ed1fc1c344dbe8d5ac6424a4237833d81f1b556',
+  'dart_revision': '4851720b30d27cb87787f09be39ae536289348a4',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py