Roll src/third_party/dart bdd9e74..4b9638a (7 commits)

dart-lang/sdk@4b9638aaa1 [VM/nnbd] Use a single byte in snapshot to write flags and nullability of types.
dart-lang/sdk@f6efefc09c [dartdevc] Move the custom type test logic to patch files
dart-lang/sdk@1994c5c323 Improve error reporting in ID tests
dart-lang/sdk@e93bf30171 fix deprecated messages for implicit getters/setters
dart-lang/sdk@b647e327aa Fix an assertion to support migration of part files
dart-lang/sdk@335b85fea1 [nnbd_migration] for tool/trial_migration, accept interest argument.
dart-lang/sdk@3e3a926690 Fix spread and Set/Map literal disambiguation when NNBD.

Author: bkonyi

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': 'bdd9e74afc1681ca7e43945e3547641321486ab7',
+  'dart_revision': '4b9638aaa17203b4e4f9ceb8492faf6a11301999',
 
   # 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

@@ -1,4 +1,4 @@
-Signature: 9eca262fe53992c95ca532d5e2e05c78
+Signature: cb6a78a49c674537ebcffa756ccdea6b
 
 UNUSED LICENSES: