Add missing IWYU message_loop.h includes.

third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl_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 "platform/scheduler/renderer/renderer_scheduler_impl.h"
 
 #include <utility>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/test/simple_test_tick_clock.h"
 #include "cc/output/begin_frame_args.h"
 #include "cc/test/ordered_simple_task_runner.h"
 #include "platform/WebTaskRunner.h"
 #include "platform/scheduler/base/real_time_domain.h"
 #include "platform/scheduler/base/test_time_source.h"
 #include "platform/scheduler/child/scheduler_tqm_delegate_for_test.h"
 #include "platform/scheduler/child/scheduler_tqm_delegate_impl.h"
 #include "platform/scheduler/renderer/auto_advancing_virtual_time_domain.h"
@@ skipping 3831 matching lines @@
   EXPECT_TRUE(
       scheduler_->MainThreadSeemsUnresponsive(responsiveness_threshold()));
   // Once we've dropped the lock, we realize the main thread is responsive.
   DropQueueingTimeEstimatorLock();
   EXPECT_FALSE(
       scheduler_->MainThreadSeemsUnresponsive(responsiveness_threshold()));
 }
 
 }  // namespace scheduler
 }  // namespace blink