Bug 734306: Fix bad conversion from nsresult to NPError. r=bas

dom/plugins/base/nsNPAPIPluginInstance.cpp

@@ -1488,7 +1488,7 @@ nsNPAPIPluginInstance::InitAsyncSurface(NPSize *size, NPImageFormat format,
   if (mOwner)
     return mOwner->InitAsyncSurface(size, format, initData, surface);
 
-  return NS_ERROR_FAILURE;
+  return NPERR_GENERIC_ERROR;
 }
 
 NPError
@@ -1497,7 +1497,7 @@ nsNPAPIPluginInstance::FinalizeAsyncSurface(NPAsyncSurface *surface)
   if (mOwner)
     return mOwner->FinalizeAsyncSurface(surface);
 
-  return NS_ERROR_FAILURE;
+  return NPERR_GENERIC_ERROR;
 }
 
 void

dom/plugins/base/nsPluginInstanceOwner.cpp

@@ -804,12 +804,12 @@ NPBool nsPluginInstanceOwner::ConvertPoint(double sourceX, double sourceY, NPCoo
 NPError nsPluginInstanceOwner::InitAsyncSurface(NPSize *size, NPImageFormat format,
                                                 void *initData, NPAsyncSurface *surface)
 {
-  return NPERR_GENERIC_ERROR;
+  return NPERR_INCOMPATIBLE_VERSION_ERROR;
 }
 
 NPError nsPluginInstanceOwner::FinalizeAsyncSurface(NPAsyncSurface *)
 {
-  return NPERR_GENERIC_ERROR;
+  return NPERR_INCOMPATIBLE_VERSION_ERROR;
 }
 
 void nsPluginInstanceOwner::SetCurrentAsyncSurface(NPAsyncSurface *, NPRect*)