Roll Dart SDK from 3cf0a5ae9d65 to 98a1f33db020 (1 revision) (#24499)

DEPS

@@ -35,7 +35,7 @@ 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': '3cf0a5ae9d65105850052d7975c6f6f41095db37',
+  'dart_revision': '98a1f33db020b51fe414fc4fe6b6f7edceb0bd11',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py