Add missing IWYU message_loop.h includes.

content/renderer/gpu/render_widget_compositor_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 "content/renderer/gpu/render_widget_compositor.h"
 
 #include <utility>
 
 #include "base/location.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/single_thread_task_runner.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "cc/animation/animation_host.h"
 #include "cc/output/begin_frame_args.h"
 #include "cc/output/copy_output_request.h"
 #include "cc/test/fake_compositor_frame_sink.h"
 #include "cc/test/test_context_provider.h"
 #include "cc/test/test_web_graphics_context_3d.h"
 #include "cc/trees/layer_tree_host.h"
@@ skipping 284 matching lines @@
 
 TEST_F(RenderWidgetCompositorFrameSinkTest, FallbackSuccessNormalSuccess) {
   // The first success is a fallback, but the next should not be a fallback.
   RunTest(false,
           RenderWidgetCompositor::COMPOSITOR_FRAME_SINK_RETRIES_BEFORE_FALLBACK,
           1, 1);
 }
 
 }  // namespace
 }  // namespace content