Roll src/third_party/dart e4344a5..a4d799c (7 commits) (flutter#14083)

dart-lang/sdk@a4d799c402 Migrate corelib/ tests starting with b-d to NNBD.
dart-lang/sdk@18a9b29687 Add a repro for issue flutter#39609
dart-lang/sdk@ec28bf1fd1 [analyzer] refactor the vm status section in the analyzer diagnostics page
dart-lang/sdk@bf69257c5f [dart:io] socket profiler in dart:io
dart-lang/sdk@1392d61c9b [infra] Modify 2.7.0 make_version hack so that it also works on other branches
dart-lang/sdk@4fe27fd444 Report an error when 'await' is used in the initializer of a late local variable.
dart-lang/sdk@6305276184 Remove deprecated 'byteStore' and 'fileContentOverlay' parameters.

Author: bkonyi

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': 'e4344a568f66ba122a172dd53c4b922a9c34502b',
+  'dart_revision': 'a4d799c402efc36327cad2f42186bb48ea9cf18a',
 
   # 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: 69a0bc4edef486cababeace42b42336a
+Signature: f8a490c0ed4d443c531bcee5cb11ff28
 
 UNUSED LICENSES: