OverscrollGlow for mainThread-{BLINK CHANGES}

Source/core/layout/LayoutBox.cpp

Index: Source/core/layout/LayoutBox.cpp
diff --git a/Source/core/layout/LayoutBox.cpp b/Source/core/layout/LayoutBox.cpp
index 4d91b4bd9785c37212fafd5e1afd160030a4e709..70a83d173130355aeb3717bd4cee3498de80d346 100644
--- a/Source/core/layout/LayoutBox.cpp
+++ b/Source/core/layout/LayoutBox.cpp
@@ -100,6 +100,7 @@ static bool skipBodyBackground(const LayoutBox* bodyElementRenderer)
 
 LayoutBox::LayoutBox(ContainerNode* node)
     : LayoutBoxModelObject(node)
+    , m_unusedDelta(IntPoint())
     , m_intrinsicContentLogicalHeight(-1)
     , m_minPreferredLogicalWidth(-1)
     , m_maxPreferredLogicalWidth(-1)
@@ -746,7 +747,15 @@ bool LayoutBox::scroll(ScrollDirection direction, ScrollGranularity granularity,
     if (!layer() || !layer()->scrollableArea())
         return false;
 
-    return layer()->scrollableArea()->scroll(direction, granularity, delta);
+    Scrollbar* scrollbar = (direction == ScrollUp || direction == ScrollDown) ? layer()->scrollableArea()->verticalScrollbar() : layer()->scrollableArea()->horizontalScrollbar();
+    IntPoint initialPoint = scrollbar ? layer()->scrollableArea()->convertFromScrollbarToContainingView(scrollbar, layer()->scrollableArea()->scrollPosition()) : IntPoint();
+    bool didScroll = layer()->scrollableArea()->scroll(direction, granularity, delta);
+    IntPoint afterScrollPoint = scrollbar ? layer()->scrollableArea()->convertFromScrollbarToContainingView(scrollbar, layer()->scrollableArea()->scrollPosition()) : IntPoint();
+    if (direction == ScrollUp || direction == ScrollDown)
+        m_unusedDelta.setY(((afterScrollPoint.y() - initialPoint.y()) + delta) * -1);
+    else if (direction == ScrollLeft || direction == ScrollRight)
+        m_unusedDelta.setX(((afterScrollPoint.x() - initialPoint.x()) + delta) * -1);
+    return didScroll;
 }
 

[majidvp, 2015/04/23 18:25:08]

unused scroll delta is already being calculated in |ScrollableArea::scroll|. 
It makes sense to re-use that instead of trying to recompute it here.
On option is to have  |ScrollableArea::scroll| also return
|ScrollResultOneDimensional| which contains unused delta.

[MuVen, 2015/04/27 12:53:46]

Done.

 bool LayoutBox::canBeScrolledAndHasScrollableArea() const