Roll src/third_party/dart 96e7a4ff30..73fdf19b56 (3 commits) (#14063)

dart-lang/sdk@73fdf19b56 [dart2js] Add variance table to RTI and updated subtyping wrt variance.
dart-lang/sdk@58dde43b5e [analysis_server] don't create futures for stalled plugins.
dart-lang/sdk@5aa86eb123 [vm/concurrency] Run all isolate related tests with/without enabling isolate groups

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': '96e7a4ff30c5850762225efca0fa1b48f28c1666',
+  'dart_revision': '73fdf19b5644b94447e8d489eb17955cc48fad67',
 
   # 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: 544b012fb76cdd196ba7ab5c8d242a54
+Signature: 29612380ad0a4881092ca5b0f0638f18
 
 UNUSED LICENSES: