Pepper takes ownership of a mailbox before passing it to the texture layer.

ppapi/proxy/ppb_graphics_3d_proxy.h

 // 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.
 
 #ifndef PPAPI_PROXY_PPB_GRAPHICS_3D_PROXY_H_
 #define PPAPI_PROXY_PPB_GRAPHICS_3D_PROXY_H_
 
 #include <stdint.h>
 
 #include <vector>
@@ skipping 37 matching lines @@
   PP_Bool SetGetBuffer(int32_t shm_id) override;
   PP_Bool Flush(int32_t put_offset) override;
   scoped_refptr<gpu::Buffer> CreateTransferBuffer(uint32_t size,
                                                   int32_t* id) override;
   PP_Bool DestroyTransferBuffer(int32_t id) override;
   gpu::CommandBuffer::State WaitForTokenInRange(int32_t start,
                                                 int32_t end) override;
   gpu::CommandBuffer::State WaitForGetOffsetInRange(int32_t start,
                                                     int32_t end) override;
   void EnsureWorkVisible() override;
+  void TakeFrontBuffer() override;
 
  private:
   // PPB_Graphics3D_Shared overrides.
   gpu::CommandBuffer* GetCommandBuffer() override;
   gpu::GpuControl* GetGpuControl() override;
   int32_t DoSwapBuffers(const gpu::SyncToken& sync_token) override;
 
   std::unique_ptr<PpapiCommandBufferProxy> command_buffer_;
 
   DISALLOW_COPY_AND_ASSIGN(Graphics3D);
@@ skipping 35 matching lines @@
                                     bool* success);
   void OnMsgAsyncFlush(const HostResource& context, int32_t put_offset);
   void OnMsgCreateTransferBuffer(
       const HostResource& context,
       uint32_t size,
       int32_t* id,
       ppapi::proxy::SerializedHandle* transfer_buffer);
   void OnMsgDestroyTransferBuffer(const HostResource& context, int32_t id);
   void OnMsgSwapBuffers(const HostResource& context,
                         const gpu::SyncToken& sync_token);
+  void OnMsgTakeFrontBuffer(const HostResource& context);
   void OnMsgEnsureWorkVisible(const HostResource& context);
   // Renderer->plugin message handlers.
   void OnMsgSwapBuffersACK(const HostResource& context,
                            int32_t pp_error);
 
   void SendSwapBuffersACKToPlugin(int32_t result,
                                   const HostResource& context);
 
   ProxyCompletionCallbackFactory<PPB_Graphics3D_Proxy> callback_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PPB_Graphics3D_Proxy);
 };
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif  // PPAPI_PROXY_PPB_GRAPHICS_3D_PROXY_H_