Roll Dart SDK from 7aa8656 to bf7e9d1 (21 revisions) (#18538)

Author: skia-flutter-autoroll

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': '7aa8656d1dd8440ec9a96d4a71b6bdb37b9f769e',
+  'dart_revision': 'bf7e9d13d730a71bd05974cc083ba0016f9e1528',
 
   # 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: a6a5873eae766b8ba9c50098ac046c7b
+Signature: 9ab6a6b95dad900c3e3ae81b83f282f1
 
 UNUSED LICENSES:
 
@@ -7446,6 +7446,7 @@ FILE: ../../../third_party/dart/sdk/lib/html/html_common/conversions_dart2js.dar
 FILE: ../../../third_party/dart/sdk/lib/html/html_common/html_common.dart
 FILE: ../../../third_party/dart/sdk/lib/libraries.json
 FILE: ../../../third_party/dart/sdk/lib/vmservice_libraries.json
+FILE: ../../../third_party/dart/sdk_nnbd/lib/_internal/allowed_experiments.json
 FILE: ../../../third_party/dart/sdk_nnbd/lib/html/html_common/conversions_dart2js.dart
 FILE: ../../../third_party/dart/sdk_nnbd/lib/html/html_common/html_common.dart
 FILE: ../../../third_party/dart/sdk_nnbd/lib/libraries.json