Fix scrollbar damage accumulation issue

Source/core/rendering/RenderLayerScrollableArea.cpp

Index: Source/core/rendering/RenderLayerScrollableArea.cpp
diff --git a/Source/core/rendering/RenderLayerScrollableArea.cpp b/Source/core/rendering/RenderLayerScrollableArea.cpp
index 052e0aa3c0c2db3ff6961f0c9a125a5eec6405b8..16da4229c57bb84dfe9dd2f93450434cb2f37b31 100644
--- a/Source/core/rendering/RenderLayerScrollableArea.cpp
+++ b/Source/core/rendering/RenderLayerScrollableArea.cpp
@@ -206,14 +206,8 @@ void RenderLayerScrollableArea::invalidateScrollbarRect(Scrollbar* scrollbar, co
     IntRect intRect = pixelSnappedIntRect(repaintRect);
 
     if (box().frameView()->isInPerformLayout()) {
-        if (scrollbar == m_vBar.get()) {
-            m_verticalBarDamage = intRect;
-            m_hasVerticalBarDamage = true;
-        } else {
-            m_horizontalBarDamage = intRect;
-            m_hasHorizontalBarDamage = true;
-        }
-
+        addScrollbarDamage(scrollbar, intRect);
+        box().setMayNeedPaintInvalidation(true);

[Julien - ping for review, 2014/07/23 20:46:23]

I don't really like this change. If we need to generate invalidation for
scrollbars that approach in https://codereview.chromium.org/403593005/ (patchset
3) was better. Alternatively shouldCheckForPaintInvalidation should be patched.

[Julien - ping for review, 2014/07/23 20:46:23]

I don't really like this change. If we need to generate invalidation for
scrollbars that approach in https://codereview.chromium.org/403593005/ (patchset
3) was better. Alternatively shouldCheckForPaintInvalidation should be patched.

[Xianzhu, 2014/07/24 00:33:48]

Removed the above statement.

     } else {
         box().invalidatePaintRectangle(intRect);
     }