Update RootFrameViewport::userScroll to distribute scrolls between viewports.

third_party/WebKit/Source/platform/scroll/ScrollableArea.h

Index: third_party/WebKit/Source/platform/scroll/ScrollableArea.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollableArea.h b/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
index bc261b77f4d9b0381eccf2bf36d5478dd6b6bae6..4a77795e4af562735cb8ffa8b34d8907bb1f92d0 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
@@ -247,7 +247,7 @@ public:
     void layerForScrollingDidChange(WebCompositorAnimationTimeline*);
 
     void cancelScrollAnimation();
-    void cancelProgrammaticScrollAnimation();
+    virtual void cancelProgrammaticScrollAnimation();
 
     virtual ~ScrollableArea();
 
@@ -276,6 +276,8 @@ public:
     // Does nothing if overlay scrollbars are enabled.
     IntSize excludeScrollbars(const IntSize&) const;
 
+    static ScrollbarOrientation scrollbarOrientationFromDirection(ScrollDirectionPhysical);

[bokan, 2015/12/04 20:42:52]

Why public? Also, just make it a normal method like scrollStep

[ymalik, 2015/12/07 17:53:14]

Done.

+
     // Need to promptly let go of owned animator objects.
     EAGERLY_FINALIZE();
     DEFINE_INLINE_VIRTUAL_TRACE() { }
@@ -283,6 +285,8 @@ public:
 protected:
     ScrollableArea();
 
+    float scrollStep(ScrollGranularity, ScrollbarOrientation) const;
+
     void setScrollOrigin(const IntPoint&);
     void resetScrollOriginChanged() { m_scrollOriginChanged = false; }