Roll Dart SDK from 960620d2e811 to 7a2a3968ef53 (12 revisions) (flutter#22778)

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': '960620d2e8118b60fe1912f5fcb752454dd99012',
+  'dart_revision': '7a2a3968ef53a46ca7c512257a449ea1319e74f2',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py
@@ -198,9 +198,6 @@ deps = {
   'src/third_party/dart/third_party/pkg/ffi':
    Var('dart_git') + '/ffi.git@a5d4232cd38562c75a3ed847baa340e399538028',
 
-  'src/third_party/dart/third_party/pkg/file':
-   Var('dart_git') + '/external/github.com/google/file.dart@0e09370f581ab6388d46fda4cdab66638c0171a1',
-
   'src/third_party/dart/third_party/pkg/fixnum':
    Var('dart_git') + '/fixnum.git@16d3890c6dc82ca629659da1934e412292508bba',
 

ci/licenses_golden/licenses_third_party

@@ -1,4 +1,4 @@
-Signature: 5a9d1e9a39cc846122fbb0b08f821335
+Signature: 85c298b5b793c191eae07f14f4ee41fc
 
 UNUSED LICENSES:
 
@@ -9095,6 +9095,10 @@ FILE: ../../../third_party/dart/benchmarks/ListCopy/dart/ListCopy.dart
 FILE: ../../../third_party/dart/benchmarks/ListCopy/dart2/ListCopy.dart
 FILE: ../../../third_party/dart/benchmarks/MD5/dart/md5.dart
 FILE: ../../../third_party/dart/benchmarks/MD5/dart2/md5.dart
+FILE: ../../../third_party/dart/benchmarks/Omnibus/dart/Omnibus.dart
+FILE: ../../../third_party/dart/benchmarks/Omnibus/dart2/Omnibus.dart
+FILE: ../../../third_party/dart/benchmarks/OmnibusDeferred/dart/OmnibusDeferred.dart
+FILE: ../../../third_party/dart/benchmarks/OmnibusDeferred/dart2/OmnibusDeferred.dart
 FILE: ../../../third_party/dart/benchmarks/RuntimeType/dart/RuntimeType.dart
 FILE: ../../../third_party/dart/benchmarks/RuntimeType/dart2/RuntimeType.dart
 FILE: ../../../third_party/dart/benchmarks/SHA1/dart/sha1.dart