Add missing IWYU message_loop.h includes.

services/service_manager/embedder/main.cc

 // Copyright 2017 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 "services/service_manager/embedder/main.h"
 
 #include "base/allocator/features.h"
 #include "base/at_exit.h"
 #include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/debug/activity_tracker.h"
 #include "base/debug/debugger.h"
 #include "base/debug/stack_trace.h"
 #include "base/i18n/icu_util.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/optional.h"
 #include "base/process/launch.h"
 #include "base/process/memory.h"
 #include "base/process/process.h"
 #include "base/run_loop.h"
 #include "base/task_scheduler/task_scheduler.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/thread.h"
 #include "base/trace_event/trace_config.h"
 #include "base/trace_event/trace_log.h"
@@ skipping 457 matching lines @@
   autorelease_pool.reset();
 #endif
 
   if (process_type == ProcessType::kEmbedder)
     delegate->ShutDownEmbedderProcess();
 
   return exit_code;
 }
 
 }  // namespace service_manager