Add missing IWYU message_loop.h includes.

components/gcm_driver/gcm_driver_desktop_unittest.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 "components/gcm_driver/gcm_driver_desktop.h"
 
 #include <stdint.h>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/location.h"
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/strings/string_util.h"
 #include "base/test/test_simple_task_runner.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "components/gcm_driver/crypto/gcm_encryption_provider.h"
 #include "components/gcm_driver/fake_gcm_app_handler.h"
 #include "components/gcm_driver/fake_gcm_client.h"
 #include "components/gcm_driver/fake_gcm_client_factory.h"
 #include "components/gcm_driver/gcm_app_handler.h"
@@ skipping 1354 matching lines @@
   PumpUILoop();
   EXPECT_EQ(GCMClient::UNKNOWN_ERROR, unregistration_result());
 
   // DeleteToken operation will be invoked after GCMClient becomes ready.
   GetGCMClient()->PerformDelayedStart();
   WaitForAsyncOperation();
   EXPECT_EQ(GCMClient::SUCCESS, unregistration_result());
 }
 
 }  // namespace gcm