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

ppapi/thunk/ppb_audio_api.h

Index: ppapi/thunk/ppb_audio_api.h
===================================================================
--- ppapi/thunk/ppb_audio_api.h	(revision 94913)
+++ ppapi/thunk/ppb_audio_api.h	(working copy)
@@ -5,6 +5,7 @@
 #ifndef PPAPI_THUNK_AUDIO_API_H_
 #define PPAPI_THUNK_AUDIO_API_H_
 
+#include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/ppb_audio.h"
 
 namespace ppapi {
@@ -17,6 +18,12 @@
   virtual PP_Resource GetCurrentConfig() = 0;
   virtual PP_Bool StartPlayback() = 0;
   virtual PP_Bool StopPlayback() = 0;
+
+  // Trusted 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