Add a template to handle properly issuing completion callbacks. This fixes

ppapi/proxy/ppb_graphics_3d_proxy.cc

 // Copyright (c) 2011 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 "ppapi/proxy/ppb_graphics_3d_proxy.h"
 
 #include "gpu/command_buffer/client/gles2_implementation.h"
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/proxy/enter_proxy.h"
 #include "ppapi/proxy/plugin_dispatcher.h"
@@ skipping 569 matching lines @@
   int shm_handle = 0;
   uint32_t shm_size = 0;
   if (enter.succeeded() &&
       enter.object()->GetTransferBuffer(id, &shm_handle, &shm_size)) {
     *transfer_buffer = TransportSHMHandleFromInt(dispatcher(), shm_handle);
     *size = shm_size;
   }
 }
 
 void PPB_Graphics3D_Proxy::OnMsgSwapBuffers(const HostResource& context) {
-  CompletionCallback callback = callback_factory_.NewOptionalCallback(
+  EnterHostFromHostResourceForceCallback<PPB_Graphics3D_API> enter(
+      context, callback_factory_,
       &PPB_Graphics3D_Proxy::SendSwapBuffersACKToPlugin, context);
-
-  EnterHostFromHostResource<PPB_Graphics3D_API> enter(context);
-  int32_t result = PP_ERROR_BADRESOURCE;
   if (enter.succeeded())
-    result = enter.object()->SwapBuffers(callback.pp_completion_callback());
-  if (result != PP_OK_COMPLETIONPENDING) {
-    // There was some error, so we won't get a flush callback. We need to now
-    // issue the ACK to the plugin hears about the error. This will also clean
-    // up the data associated with the callback.
-    callback.Run(result);
-  }
+    enter.SetResult(enter.object()->SwapBuffers(enter.callback()));
 }
 
 void PPB_Graphics3D_Proxy::OnMsgSwapBuffersACK(const HostResource& resource,
                                               int32_t pp_error) {
   EnterPluginFromHostResource<PPB_Graphics3D_API> enter(resource);
   if (enter.succeeded())
     static_cast<Graphics3D*>(enter.object())->SwapBuffersACK(pp_error);
 }
 
 void PPB_Graphics3D_Proxy::SendSwapBuffersACKToPlugin(
     int32_t result,
     const HostResource& context) {
   dispatcher()->Send(new PpapiMsg_PPBGraphics3D_SwapBuffersACK(
       INTERFACE_ID_PPB_GRAPHICS_3D, context, result));
 }
 
 }  // namespace proxy
 }  // namespace pp