PPAPI: Make blocking completion callbacks work.

ppapi/proxy/ppb_instance_proxy.cc

Index: ppapi/proxy/ppb_instance_proxy.cc
diff --git a/ppapi/proxy/ppb_instance_proxy.cc b/ppapi/proxy/ppb_instance_proxy.cc
index 88e6521f20a3f6d9c352b04ab25bd89785e17716..423876344be9c35521eb423f071fa4ec4993c386 100644
--- a/ppapi/proxy/ppb_instance_proxy.cc
+++ b/ppapi/proxy/ppb_instance_proxy.cc
@@ -436,16 +436,13 @@ PP_Bool PPB_Instance_Proxy::SetCursor(PP_Instance instance,
 }
 
 int32_t PPB_Instance_Proxy::LockMouse(PP_Instance instance,
-                                      PP_CompletionCallback callback) {
-  if (!callback.func)
-    return PP_ERROR_BADARGUMENT;
-
+                                      ApiCallbackType callback) {
   // Save the mouse callback on the instance data.
   InstanceData* data = static_cast<PluginDispatcher*>(dispatcher())->
       GetInstanceData(instance);
   if (!data)
     return PP_ERROR_BADARGUMENT;
-  if (data->mouse_lock_callback.func)
+  if (TrackedCallback::IsPending(data->mouse_lock_callback))
     return PP_ERROR_INPROGRESS;  // Already have a pending callback.
   data->mouse_lock_callback = callback;
 
@@ -691,11 +688,11 @@ void PPB_Instance_Proxy::OnPluginMsgMouseLockComplete(PP_Instance instance,
       GetInstanceData(instance);
   if (!data)
     return;  // Instance was probably deleted.
-  if (!data->mouse_lock_callback.func) {
+  if (TrackedCallback::IsPending(data->mouse_lock_callback)) {
     NOTREACHED();
     return;
   }
-  PP_RunAndClearCompletionCallback(&data->mouse_lock_callback, result);
+  TrackedCallback::ClearAndRun(&(data->mouse_lock_callback), result);
 }
 
 void PPB_Instance_Proxy::MouseLockCompleteInHost(int32_t result,