Add missing IWYU message_loop.h includes.

net/disk_cache/disk_cache_test_base.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 "net/disk_cache/disk_cache_test_base.h"
 
 #include <utility>
 
 #include "base/files/file_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/path_service.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 #include "net/base/test_completion_callback.h"
 #include "net/disk_cache/blockfile/backend_impl.h"
 #include "net/disk_cache/cache_util.h"
@@ skipping 330 matching lines @@
   if (size_)
     EXPECT_TRUE(cache_impl_->SetMaxSize(size_));
   if (new_eviction_)
     cache_impl_->SetNewEviction();
   cache_impl_->SetType(type_);
   cache_impl_->SetFlags(flags);
   net::TestCompletionCallback cb;
   int rv = cache_impl_->Init(cb.callback());
   ASSERT_THAT(cb.GetResult(rv), IsOk());
 }