Add missing IWYU message_loop.h includes.

chrome/browser/extensions/api/tabs/tabs_test.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 <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
 #include <string>
 
 #include "apps/test/app_window_waiter.h"
 #include "base/memory/ref_counted.h"
+#include "base/message_loop/message_loop.h"
 #include "base/strings/pattern.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/values.h"
 #include "build/build_config.h"
 #include "chrome/browser/apps/app_browsertest_util.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/devtools/devtools_window_testing.h"
 #include "chrome/browser/extensions/api/tabs/tabs_api.h"
@@ skipping 2167 matching lines @@
   EXPECT_TRUE(ExecuteScriptAndExtractString(
       new_contents,
       "var w = window.open('', 'old-contents');\n"
       "window.domAutomationController.send(w.location.href);",
       &location_of_other_window));
   EXPECT_EQ(old_contents->GetMainFrame()->GetLastCommittedURL().spec(),
             location_of_other_window);
 }
 
 }  // namespace extensions