Scroll only visual viewport during OSX pinch gesture behind flag.

Source/core/frame/PinchViewport.cpp

Index: Source/core/frame/PinchViewport.cpp
diff --git a/Source/core/frame/PinchViewport.cpp b/Source/core/frame/PinchViewport.cpp
index 4b20bc08d9ebbdac6c12b02cd6552e09909130d8..4bf57b5f645b9af7b020a791c6e63a6f6956ec30 100644
--- a/Source/core/frame/PinchViewport.cpp
+++ b/Source/core/frame/PinchViewport.cpp
@@ -239,11 +239,14 @@ bool PinchViewport::magnifyScaleAroundAnchor(float magnifyDelta, const FloatPoin
 
     // First try to use the anchor's delta to scroll the FrameView.
     FloatSize anchorDeltaUnusedByScroll = anchorDelta;
-    FrameView* view = mainFrame()->view();
-    DoublePoint oldPosition = view->scrollPositionDouble();
-    view->scrollBy(DoubleSize(anchorDelta.width(), anchorDelta.height()), UserScroll);
-    DoublePoint newPosition = view->scrollPositionDouble();
-    anchorDeltaUnusedByScroll = anchorDelta - toFloatSize(newPosition - oldPosition);
+
+    if (!frameHost().settings().invertViewportScrollOrder()) {
+        FrameView* view = mainFrame()->view();
+        DoublePoint oldPosition = view->scrollPositionDouble();
+        view->scrollBy(DoubleSize(anchorDelta.width(), anchorDelta.height()), UserScroll);
+        DoublePoint newPosition = view->scrollPositionDouble();
+        anchorDeltaUnusedByScroll -= toFloatSize(newPosition - oldPosition);
+    }
 
     // Manually bubble any remaining anchor delta up to the pinch viewport.
     FloatPoint newLocation(location() + anchorDeltaUnusedByScroll);