Roll src/third_party/dart a3b579d5c3..2a3b844b41 (5 commits) (#11060)

dart-lang/sdk@2a3b844b41 [vm] Disallow copy assignment for hash maps.
dart-lang/sdk@ba5c2a16bd Support completion of extension members
dart-lang/sdk@4938e4564c Migration: add support for local functions and function expressions.
dart-lang/sdk@3729f0d56f Update list.dart
dart-lang/sdk@528292bd30 Expire constant-update-2018 flag.

DEPS

@@ -34,7 +34,7 @@ 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': 'a3b579d5c32f726dcee552d8331a593ebc84812a',
+  'dart_revision': '2a3b844b41e220e99870747f53ea4016169e7178',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py

ci/licenses_golden/licenses_third_party

-Signature: f5a76c0b3e465d07eae5f422d6645b73
+Signature: 7fc580d4451fdc76fd95cabf9d7d02a7
 
 UNUSED LICENSES: