Add missing IWYU message_loop.h includes.

chrome/browser/dom_distiller/distillable_page_utils_browsertest.cc

 // Copyright 2015 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 <string.h>
 
 #include "base/command_line.h"
+#include "base/message_loop/message_loop.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/test/base/in_process_browser_test.h"
 #include "chrome/test/base/ui_test_utils.h"
 #include "components/dom_distiller/content/browser/distillable_page_utils.h"
 #include "components/dom_distiller/core/dom_distiller_switches.h"
 #include "content/public/test/browser_test_utils.h"
 #include "content/public/test/test_utils.h"
@@ skipping 178 matching lines @@
   {
     testing::InSequence dummy;
     EXPECT_CALL(holder_, OnResult(false, false)).Times(1);
     EXPECT_CALL(holder_, OnResult(false, true))
         .WillOnce(testing::InvokeWithoutArgs(QuitSoon));
     NavigateAndWait(kNonArticlePath, 0);
   }
 }
 
 }  // namespace dom_distiller