Manual roll of Dart 6d4e7d6830...021a49e88c (flutter#19074)

* 1. Manual roll of Dart 6d4e7d6830...021a49e88c

dart-lang/sdk@021a49e88c Update the way to get feature set and language version.
dart-lang/sdk@d1638508c1 Migration: streamline behavior injection in migration_cli_test.dart.

2. Update ICU dependency and adjust license script to account for this
   change.

* Update license tool signature.

Author: a-siva

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': '6d4e7d6830f3e417914dc33583c727975123c3e4',
+  'dart_revision': '021a49e88c0df775ca289885cf513e358337c394',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py
@@ -148,7 +148,7 @@ deps = {
    Var('chromium_git') + '/chromium/src/ios.git' + '@' + Var('ios_tools_revision'),
 
   'src/third_party/icu':
-   Var('chromium_git') + '/chromium/deps/icu.git' + '@' + '5005010d694e16571b8dfbf07d70817841f80a69',
+   Var('chromium_git') + '/chromium/deps/icu.git' + '@' + '8d29692df640668ed7e4d1817715440c4e05697a',
 
   'src/third_party/khronos':
    Var('chromium_git') + '/chromium/src/third_party/khronos.git' + '@' + '7122230e90547962e0f0c627f62eeed3c701f275',