Bug 1266154 - Don't start a scroll snap animation if we're already at the destination. r=kats

MozReview-Commit-ID: EP7s414NQ4K

--HG--
extra : rebase_source : 3f57b46f1e23c69f1efd7039fada2b8c60cd7f4b
extra : amend_source : 580e1a95597e6c9fe56e3b655f52c7817e391df2

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -3966,7 +3966,9 @@ Maybe<CSSPoint> AsyncPanZoomController::FindSnapPointNear(
 void AsyncPanZoomController::ScrollSnapNear(const CSSPoint& aDestination) {
   if (Maybe<CSSPoint> snapPoint =
         FindSnapPointNear(aDestination, nsIScrollableFrame::DEVICE_PIXELS)) {
-    SmoothScrollTo(*snapPoint);
+    if (*snapPoint != mFrameMetrics.GetScrollOffset()) {
+      SmoothScrollTo(*snapPoint);
+    }
   }
 }