Fix flakiness in postMessage-related SitePerProcessBrowserTests.

content/public/test/browser_test_utils.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/public/test/browser_test_utils.h"
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/json/json_reader.h"
@@ skipping 57 matching lines @@
     registrar_.Add(this, NOTIFICATION_DOM_OPERATION_RESPONSE,
                    Source<WebContents>(web_contents()));
     message_loop_runner_ = new MessageLoopRunner;
   }
 
   void Observe(int type,
                const NotificationSource& source,
                const NotificationDetails& details) override {
     DCHECK(type == NOTIFICATION_DOM_OPERATION_RESPONSE);
     Details<DomOperationNotificationDetails> dom_op_details(details);
-    response_ = dom_op_details->json;
-    did_respond_ = true;
-    message_loop_runner_->Quit();
+    if (!did_respond_) {
+      response_ = dom_op_details->json;
+      did_respond_ = true;
+      message_loop_runner_->Quit();
+    }
   }
 
   // Overridden from WebContentsObserver:
   void RenderProcessGone(base::TerminationStatus status) override {
     message_loop_runner_->Quit();
   }
 
   bool WaitAndGetResponse(std::string* response) WARN_UNUSED_RESULT {
     message_loop_runner_->Run();
     *response = response_;
@@ skipping 894 matching lines @@
 void FrameWatcher::WaitFrames(int frames_to_wait) {
   if (frames_to_wait <= 0)
     return;
   base::RunLoop run_loop;
   base::AutoReset<base::Closure> reset_quit(&quit_, run_loop.QuitClosure());
   base::AutoReset<int> reset_frames_to_wait(&frames_to_wait_, frames_to_wait);
   run_loop.Run();
 }
 
 }  // namespace content