Update RootFrameViewport::userScroll to distribute scrolls between viewports.

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

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 112 matching lines @@
         m_scrollOrigin = origin;
         m_scrollOriginChanged = true;
     }
 }
 
 GraphicsLayer* ScrollableArea::layerForContainer() const
 {
     return layerForScrolling() ? layerForScrolling()->parent() : 0;
 }
 
+ScrollbarOrientation ScrollableArea::scrollbarOrientationFromDirection(ScrollDirectionPhysical direction) const
+{
+    return (direction == ScrollUp  || direction == ScrollDown) ? VerticalScrollbar : HorizontalScrollbar;
+}
+
+float ScrollableArea::scrollStep(ScrollGranularity granularity, ScrollbarOrientation orientation) const
+{
+    switch (granularity) {
+    case ScrollByLine:
+        return lineStep(orientation);
+    case ScrollByPage:
+        return pageStep(orientation);
+    case ScrollByDocument:
+        return documentStep(orientation);
+    case ScrollByPixel:
+    case ScrollByPrecisePixel:
+        return pixelStep(orientation);
+    default:
+        ASSERT_NOT_REACHED();
+        return 0.0f;
+    }
+}
+
 ScrollResultOneDimensional ScrollableArea::userScroll(ScrollDirectionPhysical direction, ScrollGranularity granularity, float delta)
 {
-    ScrollbarOrientation orientation;
-    if (direction == ScrollUp || direction == ScrollDown)
-        orientation = VerticalScrollbar;
-    else
-        orientation = HorizontalScrollbar;
-
+    ScrollbarOrientation orientation = scrollbarOrientationFromDirection(direction);
     if (!userInputScrollable(orientation))
         return ScrollResultOneDimensional(false, delta);
 
     cancelProgrammaticScrollAnimation();
 
-    float step = 0;
-    switch (granularity) {
-    case ScrollByLine:
-        step = lineStep(orientation);
-        break;
-    case ScrollByPage:
-        step = pageStep(orientation);
-        break;
-    case ScrollByDocument:
-        step = documentStep(orientation);
-        break;
-    case ScrollByPixel:
-    case ScrollByPrecisePixel:
-        step = pixelStep(orientation);
-        break;
-    }
+    float step = scrollStep(granularity, orientation);
 
     if (direction == ScrollUp || direction == ScrollLeft)
         delta = -delta;
 
     return scrollAnimator().userScroll(orientation, granularity, step, delta);
 }
 
 void ScrollableArea::setScrollPosition(const DoublePoint& position, ScrollType scrollType, ScrollBehavior behavior)
 {
     if (behavior == ScrollBehaviorAuto)
@@ skipping 395 matching lines @@
 
 }
 
 DEFINE_TRACE(ScrollableArea)
 {
     visitor->trace(m_scrollAnimator);
     visitor->trace(m_programmaticScrollAnimator);
 }
 
 } // namespace blink