Mac: Update scrollbar size and input position during impl-overscroll

Source/core/frame/FrameView.h

Index: Source/core/frame/FrameView.h
diff --git a/Source/core/frame/FrameView.h b/Source/core/frame/FrameView.h
index 814ee26da913ab2f3ff5e552592105080d854a42..fbda1aa028e1f244e0e6847a8c9342750d23fbaf 100644
--- a/Source/core/frame/FrameView.h
+++ b/Source/core/frame/FrameView.h
@@ -167,6 +167,9 @@ public:
     virtual bool rubberBandingOnCompositorThread() const override;
     void setScrollPositionNonProgrammatically(const IntPoint&);
 
+    FloatSize elasticOverscroll() const { return m_elasticOverscroll; }
+    void setElasticOverscroll(const FloatSize&);
+
     // This is different than visibleContentRect() in that it ignores negative (or overly positive)
     // offsets from rubber-banding, and it takes zooming into account.
     LayoutRect viewportConstrainedVisibleContentRect() const;
@@ -801,6 +804,8 @@ private:
     int m_scrollbarsAvoidingResizer;
     bool m_scrollbarsSuppressed;
 
+    FloatSize m_elasticOverscroll;
+
     bool m_inUpdateScrollbars;
 
     IntPoint m_panScrollIconPoint;