Roll Dart SDK from 8e089c6 to 866f5cf (1 revision) (flutter#37278)

Author: skia-flutter-autoroll

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': '8e089c61be5842bd63d1767eb9366584ee19a963',
+  'dart_revision': '866f5cfad18a837ced18b343b7576582085c34bf',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py