Convert asynchronous closure test in cr.ui framework to a browser test.

content/public/test/browser_test_utils.cc

Index: content/public/test/browser_test_utils.cc
diff --git a/content/public/test/browser_test_utils.cc b/content/public/test/browser_test_utils.cc
index b7db17d055591c3e5ba6607ecd490f34cdf4b86c..bfa37adee1a606c6f5fd0dd91529f1bf57fa5e48 100644
--- a/content/public/test/browser_test_utils.cc
+++ b/content/public/test/browser_test_utils.cc
@@ -506,6 +506,7 @@ bool DOMMessageQueue::WaitForMessage(std::string* message) {
     return false;
   if (message)
     *message = message_queue_.front();
+  message_queue_.pop();
   return true;
 }