Bug 1421380 - Don't do a composite of WR rendered frames unless a composite is requested. r=nical

We sometimes render frames for hit-testing consistency requirements but
those frames don't need compositing. This goes with webrender PR 2358.

MozReview-Commit-ID: D6DRF040D5a

--HG--
extra : rebase_source : fd5dadc35a6f6a54b385f535d4ae9c6e34f3a779

gfx/webrender_bindings/src/bindings.rs

@@ -481,7 +481,7 @@ impl RenderNotifier for CppNotifier {
         unsafe {
             if scrolled {
                 wr_notifier_new_scroll_frame_ready(self.window_id, composite_needed);
-            } else {
+            } else if composite_needed {
                 wr_notifier_new_frame_ready(self.window_id);
             }
         }