Roll Dart SDK from 2cddb14dc9a9 to a171b36d2fdd (1 revision) (flutter#27846)

Author: skia-flutter-autoroll

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': '2cddb14dc9a9d57361f936c425df48a951751c08',
+  'dart_revision': 'a171b36d2fddeac990b29b13837abdb69a37f786',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py