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

ppapi/thunk/ppb_audio_thunk.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/thunk/thunk.h"
 #include "ppapi/thunk/enter.h"
 #include "ppapi/thunk/ppb_audio_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
 namespace ppapi {
 namespace thunk {
 
 namespace {
 
+typedef EnterResource<PPB_Audio_API> EnterAudio;
+
 PP_Resource Create(PP_Instance instance,
                    PP_Resource config_id,
                    PPB_Audio_Callback callback,
                    void* user_data) {
   EnterFunction<ResourceCreationAPI> enter(instance, true);
   if (enter.failed())
     return 0;
   return enter.functions()->CreateAudio(instance, config_id,
                                         callback, user_data);
 }
 
 PP_Bool IsAudio(PP_Resource resource) {
-  EnterResource<PPB_Audio_API> enter(resource, false);
+  EnterAudio enter(resource, false);
   return enter.succeeded() ? PP_TRUE : PP_FALSE;
 }
 
 PP_Resource GetCurrentConfiguration(PP_Resource audio_id) {
-  EnterResource<PPB_Audio_API> enter(audio_id, true);
+  EnterAudio enter(audio_id, true);
   if (enter.failed())
     return 0;
   return enter.object()->GetCurrentConfig();
 }
 
 PP_Bool StartPlayback(PP_Resource audio_id) {
-  EnterResource<PPB_Audio_API> enter(audio_id, true);
+  EnterAudio enter(audio_id, true);
   if (enter.failed())
     return PP_FALSE;
   return enter.object()->StartPlayback();
 }
 
 PP_Bool StopPlayback(PP_Resource audio_id) {
-  EnterResource<PPB_Audio_API> enter(audio_id, true);
+  EnterAudio enter(audio_id, true);
   if (enter.failed())
     return PP_FALSE;
   return enter.object()->StopPlayback();
 }
 
 const PPB_Audio g_ppb_audio_thunk = {
   &Create,
   &IsAudio,
   &GetCurrentConfiguration,
   &StartPlayback,
   &StopPlayback
 };
 
 }  // namespace
 
 const PPB_Audio* GetPPB_Audio_Thunk() {
   return &g_ppb_audio_thunk;
 }
 
 }  // namespace thunk
 }  // namespace ppapi