Add missing IWYU message_loop.h includes.

chromeos/process_proxy/process_proxy_registry.cc

 // Copyright (c) 2012 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 "chromeos/process_proxy/process_proxy_registry.h"
 
 #include "base/bind.h"
+#include "base/message_loop/message_loop.h"
 
 namespace chromeos {
 
 namespace {
 
 const char kWatcherThreadName[] = "ProcessWatcherThread";
 
 const char kStdoutOutputType[] = "stdout";
 const char kExitOutputType[] = "exit";
 
@@ skipping 150 matching lines @@
 
   // TODO(tbarzic): Change process output watcher to watch for fd readability on
   //    FILE thread, and move output reading to worker thread instead of
   //    spinning a new thread.
   watcher_thread_.reset(new base::Thread(kWatcherThreadName));
   return watcher_thread_->StartWithOptions(
       base::Thread::Options(base::MessageLoop::TYPE_IO, 0));
 }
 
 }  // namespace chromeos