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

ppapi/thunk/ppb_audio_trusted_thunk.cc

Index: ppapi/thunk/ppb_audio_trusted_thunk.cc
===================================================================
--- ppapi/thunk/ppb_audio_trusted_thunk.cc	(revision 94913)
+++ ppapi/thunk/ppb_audio_trusted_thunk.cc	(working copy)
@@ -3,10 +3,11 @@
 // found in the LICENSE file.
 
 #include "ppapi/c/pp_errors.h"
+#include "ppapi/c/trusted/ppb_audio_trusted.h"
 #include "ppapi/thunk/common.h"
 #include "ppapi/thunk/enter.h"
 #include "ppapi/thunk/thunk.h"
-#include "ppapi/thunk/ppb_audio_trusted_api.h"
+#include "ppapi/thunk/ppb_audio_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
 namespace ppapi {
@@ -14,6 +15,8 @@
 
 namespace {
 
+typedef EnterResource<PPB_Audio_API> EnterAudio;
+
 PP_Resource Create(PP_Instance instance_id) {
   EnterFunction<ResourceCreationAPI> enter(instance_id, true);
   if (enter.failed())
@@ -24,7 +27,7 @@
 int32_t Open(PP_Resource audio_id,
              PP_Resource config_id,
              PP_CompletionCallback create_callback) {
-  EnterResource<PPB_AudioTrusted_API> enter(audio_id, true);
+  EnterAudio enter(audio_id, true);
   if (enter.failed())
     return MayForceCallback(create_callback, PP_ERROR_BADRESOURCE);
   int32_t result = enter.object()->OpenTrusted(config_id, create_callback);
@@ -32,7 +35,7 @@
 }
 
 int32_t GetSyncSocket(PP_Resource audio_id, int* sync_socket) {
-  EnterResource<PPB_AudioTrusted_API> enter(audio_id, true);
+  EnterAudio enter(audio_id, true);
   if (enter.failed())
     return PP_ERROR_BADRESOURCE;
   return enter.object()->GetSyncSocket(sync_socket);
@@ -41,7 +44,7 @@
 int32_t GetSharedMemory(PP_Resource audio_id,
                         int* shm_handle,
                         uint32_t* shm_size) {
-  EnterResource<PPB_AudioTrusted_API> enter(audio_id, true);
+  EnterAudio enter(audio_id, true);
   if (enter.failed())
     return PP_ERROR_BADRESOURCE;
   return enter.object()->GetSharedMemory(shm_handle, shm_size);