doc imports for enum values (#151548)

To verify that https://github.com/dart-lang/sdk/commit/a9e6fefa917a4cd0191853cd3f31dd21d87e5d04 works.

Part of https://github.com/flutter/flutter/issues/150800.
https://dart.googlesource.com/external/github.com/flutter/flutter/+/a1bd8434b555aa75cf20d482d9591c50cd4306d5

DEPS

diff --git a/DEPS b/DEPS
index 62d7e09..da782c8 100644
--- a/DEPS
+++ b/DEPS
@@ -284,7 +284,7 @@
 
   'engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '45d05b714fd20485dc36b6272cc0c83b31321617',
 
-  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + 'bb637f3128e171ab51a3952584e1208718ab0396',
+  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + 'a1bd8434b555aa75cf20d482d9591c50cd4306d5',
 
   'engine/src/flutter/third_party/depot_tools':
   Var('chromium_git') + '/chromium/tools/depot_tools.git' + '@' + '580b4ff3f5cd0dcaa2eacda28cefe0f45320e8f7',

commits.json

diff --git a/commits.json b/commits.json
index 1de30fd..caa3d6e 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "engine/src/flutter":"b369582a94f1204f51bc913eeaa30f250602501e",
   "engine/src/flutter/third_party/dart":"45d05b714fd20485dc36b6272cc0c83b31321617",
-  "flutter":"bb637f3128e171ab51a3952584e1208718ab0396"
+  "flutter":"a1bd8434b555aa75cf20d482d9591c50cd4306d5"
 }
\ No newline at end of file