Roll Dart SDK from b59de86059f3 to 2a78a2978983 (1 revision) (#23179)

diff --git a/DEPS b/DEPS
index 0eace6d..9aa61dd 100644
--- a/DEPS
+++ b/DEPS
@@ -34,7 +34,7 @@
   # 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': 'b59de86059f30174a8d19ea076387072597c1a62',
+  'dart_revision': '2a78a297898350495071345b3febb0065cac54c8',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py
@@ -61,7 +61,7 @@
   'dart_stream_channel_tag': 'd7251e61253ec389ee6e045ee1042311bced8f1d',
   'dart_typed_data_tag': 'f94fc57b8e8c0e4fe4ff6cfd8290b94af52d3719',
   'dart_usage_tag': '16fbfd90c58f16e016a295a880bc722d2547d2c9',
-  'dart_watcher_rev': '64e254eba16f56d41f10d72c0b1cb24e130e1f8b',
+  'dart_watcher_rev': '1fb0a84acd8d195103f10aba03ba6bd6fdb424e5',
 
   'ocmock_tag': 'v3.7.1',
 
diff --git a/ci/licenses_golden/licenses_third_party b/ci/licenses_golden/licenses_third_party
index 2efe761..17f2d2d 100644
--- a/ci/licenses_golden/licenses_third_party
+++ b/ci/licenses_golden/licenses_third_party
@@ -1,4 +1,4 @@
-Signature: 06b8dc046306f897ef36bb7219a8b583
+Signature: 0921fca7ab9d67107e4b13df1df58fc4
 
 UNUSED LICENSES: