Add missing IWYU message_loop.h includes.

content/public/test/javascript_test_observer.cc

 // Copyright 2014 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/javascript_test_observer.h"
 
+#include "base/message_loop/message_loop.h"
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/test/test_utils.h"
 
 namespace content {
 
 TestMessageHandler::TestMessageHandler() : ok_(true) {
 }
 
@@ skipping 65 matching lines @@
 
 void JavascriptTestObserver::EndTest() {
   finished_ = true;
   if (running_) {
     running_ = false;
     base::MessageLoopForUI::current()->QuitWhenIdle();
   }
 }
 
 }  // namespace content