Add missing IWYU message_loop.h includes.

base/test/test_io_thread.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 "base/test/test_io_thread.h"
 
 #include "base/logging.h"
+#include "base/message_loop/message_loop.h"
 
 namespace base {
 
 TestIOThread::TestIOThread(Mode mode)
     : io_thread_("test_io_thread"), io_thread_started_(false) {
   switch (mode) {
     case kAutoStart:
       Start();
       return;
     case kManualStart:
@@ skipping 18 matching lines @@
   io_thread_.Stop();
   io_thread_started_ = false;
 }
 
 void TestIOThread::PostTask(const tracked_objects::Location& from_here,
                             const base::Closure& task) {
   task_runner()->PostTask(from_here, task);
 }
 
 }  // namespace base