Roll Dart SDK to 54bd8a79c48b4346d926ab3d3c3f986e5e691bc3 (#3708)

DEPS

@@ -28,7 +28,7 @@ vars = {
   # dependencies of Dart are also updated to match the entries in the
   # Dart SDK's DEPS file for that revision of Dart. The DEPS file for
   # Dart is: https://github.com/dart-lang/sdk/blob/master/DEPS
-  'dart_revision': '425626363a0c8f80cd8861fa5c7ee9eba121533a',
+  'dart_revision': '54bd8a79c48b4346d926ab3d3c3f986e5e691bc3',
   # Dart calls the next one "boringssl_gen_rev"
   'dart_boringssl_gen_revision': '753224969dbe43dad29343146529727b5066c0f3',
   # Dart calls the next one "boringssl_rev"

travis/licenses_golden/licenses_dart

-Signature: 01dbc1899b46fdc23da42e219822b51e
+Signature: 209a690ccefc1f4805cd9c9f76972812
 
 UNUSED LICENSES: