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

ppapi/proxy/ppb_graphics_3d_proxy.h

Index: ppapi/proxy/ppb_graphics_3d_proxy.h
diff --git a/ppapi/proxy/ppb_graphics_3d_proxy.h b/ppapi/proxy/ppb_graphics_3d_proxy.h
index fab0122c6478487fdd1ab8c6dfd82d69a0438951..2a28fce80b8d239ecf917439c8b4380caa53bc0c 100644
--- a/ppapi/proxy/ppb_graphics_3d_proxy.h
+++ b/ppapi/proxy/ppb_graphics_3d_proxy.h
@@ -55,6 +55,7 @@ class PPAPI_PROXY_EXPORT Graphics3D : public PPB_Graphics3D_Shared {
   gpu::CommandBuffer::State WaitForGetOffsetInRange(int32_t start,
                                                     int32_t end) override;
   void EnsureWorkVisible() override;
+  void TakeFrontBuffer() override;
 
  private:
   // PPB_Graphics3D_Shared overrides.
@@ -110,6 +111,7 @@ class PPB_Graphics3D_Proxy : public InterfaceProxy {
   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,