Move a bunch of child-only code from content/common to content/child

content/common/thread_safe_sender.h

-// Copyright (c) 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.
-
-#ifndef CONTENT_COMMON_THREAD_SAFE_SENDER_H_
-#define CONTENT_COMMON_THREAD_SAFE_SENDER_H_
-
-#include "base/memory/ref_counted.h"
-#include "ipc/ipc_sender.h"
-
-namespace base {
-class MessageLoopProxy;
-}
-
-namespace IPC {
-class SyncMessageFilter;
-}
-
-namespace content {
-class ChildThread;
-
-// The class of Sender returned by ChildThread::thread_safe_sender().
-class ThreadSafeSender
-    : public IPC::Sender,
-      public base::RefCountedThreadSafe<ThreadSafeSender> {
- public:
-  virtual bool Send(IPC::Message* msg) OVERRIDE;
-
- private:
-  friend class ChildThread;  // for construction
-  friend class base::RefCountedThreadSafe<ThreadSafeSender>;
-
-  ThreadSafeSender(base::MessageLoopProxy* main_loop,
-                   IPC::SyncMessageFilter* sync_filter);
-  virtual ~ThreadSafeSender();
-
-  scoped_refptr<base::MessageLoopProxy> main_loop_;
-  scoped_refptr<IPC::SyncMessageFilter> sync_filter_;
-
-  DISALLOW_COPY_AND_ASSIGN(ThreadSafeSender);
-};
-
-}  // namespace content
-
-#endif  // CONTENT_COMMON_THREAD_SAFE_SENDER_H_