Roll src/third_party/dart adfa4791fc..caa8747a37 (2 commits)

caa8747a37 Rework dartfix NNBD fix to use new NullabilityMigration engine
ae5bd68570 Lower relevance of deprecated suggestion sets.

DEPS

@@ -31,7 +31,7 @@ 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': 'adfa4791fcf2337c27f3aabe8a3b9d6ed0605ff1',
+  'dart_revision': 'caa8747a377778f4349ff416d6e9aa7a7e410837',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py