Bug 1571837. Don't call FlushItem for hit test items. r=mstange

We already skip painting hit test items. We can do even better
by not including them in the recording at all.

Differential Revision: https://phabricator.services.mozilla.com/D40859

--HG--
extra : moz-landing-system : lando

gfx/layers/wr/WebRenderCommandBuilder.cpp

@@ -836,10 +836,11 @@ struct DIGroup {
                                      aResources);
       } else {
         nsPaintedDisplayItem* paintedItem = item->AsPaintedDisplayItem();
-        if (dirty && paintedItem &&
+        if (paintedItem &&
             // Hit test items don't have anything to paint so skip them.
             // Ideally we would drop these items earlier...
             item->GetType() != DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO) {
+          if (dirty) {
             // What should the clip settting strategy be? We can set the full clip
             // everytime. this is probably easiest for now. An alternative would
             // be to put the push and the pop into separate items and let
@@ -869,6 +870,7 @@ struct DIGroup {
         }
       }
     }
+  }
 
   ~DIGroup() {
     GP("Group destruct\n");