Bug 1522724 - Don't clobber visualScrollOffsetUpdate flag if the visual scroll update is higher priority. r=kats,botond

We need to do both of updates in the case where both updates in the same
transaction.

Differential Revision: https://phabricator.services.mozilla.com/D17582

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

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -4285,7 +4285,9 @@ void AsyncPanZoomController::NotifyLayersUpdated(
   // locations (via e.g. both updates being eRestore).
   bool visualScrollOffsetUpdated =
       aLayerMetrics.GetVisualScrollUpdateType() != FrameMetrics::eNone;
-  if (aLayerMetrics.GetScrollUpdateType() == FrameMetrics::eMainThread ||
+  if ((aLayerMetrics.GetScrollUpdateType() == FrameMetrics::eMainThread &&
+       aLayerMetrics.GetVisualScrollUpdateType() !=
+           FrameMetrics::eMainThread) ||
       smoothScrollRequested) {
     visualScrollOffsetUpdated = false;
   }