Use gpu::Mailbox in IPCs instead of std::string

cc/texture_mailbox.h

 // 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.
 
 #ifndef CC_TEXTURE_MAILBOX_H_
 #define CC_TEXTURE_MAILBOX_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "cc/cc_export.h"
 #include "gpu/command_buffer/common/mailbox.h"
 
 namespace cc {
 
 class CC_EXPORT TextureMailbox {
  public:
   typedef base::Callback<void(unsigned)> ReleaseCallback;
   TextureMailbox();
-  TextureMailbox(const std::string& mailbox_name,
-                 const ReleaseCallback& callback);
   TextureMailbox(const gpu::Mailbox& mailbox_name,
                  const ReleaseCallback& callback);
   TextureMailbox(const gpu::Mailbox& mailbox_name,
                  const ReleaseCallback& callback,
                  unsigned sync_point);
 
   ~TextureMailbox();
 
   const ReleaseCallback& callback() const { return callback_; }
   const int8* data() const { return name_.name; }
   bool Equals(const gpu::Mailbox&) const;
   bool Equals(const TextureMailbox&) const;
   bool IsEmpty() const;
   const gpu::Mailbox& name() const { return name_; }
   void ResetSyncPoint() { sync_point_ = 0; }
   void RunReleaseCallback(unsigned sync_point) const;
   void SetName(const gpu::Mailbox&);
   unsigned sync_point() const { return sync_point_; }
 
  private:
   gpu::Mailbox name_;
   ReleaseCallback callback_;
   unsigned sync_point_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEXTURE_MAILBOX_H_