Add missing IWYU message_loop.h includes.

content/renderer/render_thread_impl_browsertest.cc

 // Copyright 2013 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/render_thread_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <utility>
 
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/debug/leak_annotations.h"
 #include "base/location.h"
 #include "base/memory/discardable_memory.h"
+#include "base/message_loop/message_loop.h"
 #include "base/metrics/field_trial.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "cc/output/buffer_to_texture_target_map.h"
 #include "content/app/mojo/mojo_init.h"
 #include "content/common/in_process_child_thread_params.h"
 #include "content/common/resource_messages.h"
@@ skipping 370 matching lines @@
                        // These formats are guaranteed to work on all platforms.
                        ::testing::Values(gfx::BufferFormat::R_8,
                                          gfx::BufferFormat::BGR_565,
                                          gfx::BufferFormat::RGBA_4444,
                                          gfx::BufferFormat::RGBA_8888,
                                          gfx::BufferFormat::BGRA_8888,
                                          gfx::BufferFormat::YVU_420)));
 
 }  // namespace
 }  // namespace content