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

ppapi/thunk/ppb_audio_trusted_api.h

Index: ppapi/thunk/ppb_audio_trusted_api.h
===================================================================
--- ppapi/thunk/ppb_audio_trusted_api.h	(revision 94913)
+++ ppapi/thunk/ppb_audio_trusted_api.h	(working copy)
@@ -1,27 +0,0 @@
-// 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.
-
-#ifndef PPAPI_THUNK_AUDIO_TRUSTED_API_H_
-#define PPAPI_THUNK_AUDIO_TRUSTED_API_H_
-
-#include "ppapi/c/trusted/ppb_audio_trusted.h"
-#include "ppapi/c/ppb_audio.h"
-
-namespace ppapi {
-namespace thunk {
-
-class PPB_AudioTrusted_API {
- public:
-  virtual ~PPB_AudioTrusted_API() {}
-
-  virtual int32_t OpenTrusted(PP_Resource config_id,
-                              PP_CompletionCallback create_callback) = 0;
-  virtual int32_t GetSyncSocket(int* sync_socket) = 0;
-  virtual int32_t GetSharedMemory(int* shm_handle, uint32_t* shm_size) = 0;
-};
-
-}  // namespace thunk
-}  // namespace ppapi
-
-#endif  // PPAPI_THUNK_AUDIO_TRUSTED_API_H_