Fix scrollbar damage accumulation issue

Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 2326 matching lines @@
     }
     frame().loader().client()->didChangeScrollOffset();
 }
 
 void FrameView::invalidateScrollbarRect(Scrollbar* scrollbar, const IntRect& rect)
 {
     // Add in our offset within the FrameView.
     IntRect dirtyRect = rect;
     dirtyRect.moveBy(scrollbar->location());
 
-    if (isInPerformLayout()) {
-        if (scrollbar == verticalScrollbar()) {
-            m_verticalBarDamage = dirtyRect;
-            m_hasVerticalBarDamage = true;
-        } else {
-            m_horizontalBarDamage = dirtyRect;
-            m_hasHorizontalBarDamage = true;
-        }
-    } else {
+    if (isInPerformLayout())
+        addScrollbarDamage(scrollbar, rect);
+    else
         invalidateRect(dirtyRect);
-    }
 }
 
 void FrameView::getTickmarks(Vector<IntRect>& tickmarks) const
 {
     if (!m_tickmarks.isEmpty())
         tickmarks = m_tickmarks;
     else
         tickmarks = frame().document()->markers().renderedRectsForMarkers(DocumentMarker::TextMatch);
 }
 
@@ skipping 927 matching lines @@
 void FrameView::willRemoveScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)
 {
     ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
     if (AXObjectCache* cache = axObjectCache()) {
         cache->remove(scrollbar);
         cache->handleScrollbarUpdate(this);
     }
 }
 
 } // namespace blink