Roll src/third_party/dart 8bdca37e98..51016532e8 (21 commits)

dart-lang/sdk@51016532e8 DEPS: update d8 to 7.8.279
dart-lang/sdk@11b1433756 Allow downwards inference of sound constructor calls.
dart-lang/sdk@c06674e558 Apply review feedback from:
dart-lang/sdk@1d90df9279 Migrate recent changes in sdk/BUILD.gn to sdk_nnbd/BUILD.gn.
dart-lang/sdk@e9c57d2e04 [dart2js] New RTI: Lower is-checks to `instanceof` in-place where possible.
dart-lang/sdk@5134490b78 [analysis_server] add crash reporting
dart-lang/sdk@af37dcf540 [analyzer] remove older crash reporting from the dartanalyzer cli
dart-lang/sdk@1d774abeea [analysis_server] Remove old crash reporting
dart-lang/sdk@1b947a51cc [dart2js] new-rti: Copy environment input type before refinement removal
dart-lang/sdk@e31c7ff591 [vm/concurrency] Move idle timeout detection from message handler to [Isolate]
dart-lang/sdk@f908fb67ce [ VM / Service ] Fix potential race in service test helper
dart-lang/sdk@1f8ef384d9 [vm] First pieces of late modifier implementation.
dart-lang/sdk@b8cd8eee5d Migrate dart:internal to NNBD.
dart-lang/sdk@d3f19cf7ae Reland "Enable visibleForTesting on unnamed constructors"
dart-lang/sdk@e65d95e8c8 (dart2js) add indirect dynamic calls to global inference and use it to model operator==
dart-lang/sdk@9ba71b0fdd Modify local inference to generate constraints with respect to variance.
dart-lang/sdk@689447d0fb Revert "[ddk] Don't use Library.isExternal"
dart-lang/sdk@8b050df2db [infra] Remove duplicate args_tag from DEPS
dart-lang/sdk@2db4368eb8 [infra] Update CHANGELOG.md for 2.6.0
dart-lang/sdk@d635bdd49c [cfe] Move variance tests to general/
dart-lang/sdk@9ddad67f73 [vm] Add aot option to protobuf_aware_treeshaker.

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': '8bdca37e98a59bdb7f52daea9da838b1a60c1cdf',
+  'dart_revision': '51016532e804570dd62edd5445768c49ad6e27f7',
 
   # 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: 62624acd0f795337602c13cd2e2e2fdf
+Signature: 2a5fa516e6ddf01f0e8048becd7a8037
 
 UNUSED LICENSES: