Fix scrollbar damage accumulation issue

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 29 matching lines @@
 
 #include "platform/TraceEvent.h"
 
 static const int kPixelsPerLineStep = 40;
 static const float kMinFractionToStepWhenPaging = 0.875f;
 
 namespace blink {
 
 struct SameSizeAsScrollableArea {
     virtual ~SameSizeAsScrollableArea();
-    unsigned damageBits : 2;
     IntRect scrollbarDamage[2];
     void* pointer;
     unsigned bitfields : 16;
     IntPoint origin;
 };
 
 COMPILE_ASSERT(sizeof(ScrollableArea) == sizeof(SameSizeAsScrollableArea), ScrollableArea_should_stay_small);
 
 int ScrollableArea::pixelsPerLineStep()
 {
     return kPixelsPerLineStep;
 }
 
 float ScrollableArea::minFractionToStepWhenPaging()
 {
     return kMinFractionToStepWhenPaging;
 }
 
 int ScrollableArea::maxOverlapBetweenPages()
 {
     static int maxOverlapBetweenPages = ScrollbarTheme::theme()->maxOverlapBetweenPages();
     return maxOverlapBetweenPages;
 }
 
 ScrollableArea::ScrollableArea()
-    : m_hasHorizontalBarDamage(false)
-    , m_hasVerticalBarDamage(false)
-    , m_constrainsScrollingToContentEdge(true)
+    : m_constrainsScrollingToContentEdge(true)
     , m_inLiveResize(false)
     , m_verticalScrollElasticity(ScrollElasticityNone)
     , m_horizontalScrollElasticity(ScrollElasticityNone)
     , m_scrollbarOverlayStyle(ScrollbarOverlayStyleDefault)
     , m_scrollOriginChanged(false)
 {
 }
 
 ScrollableArea::~ScrollableArea()
 {
@@ skipping 384 matching lines @@
 {
     return scrollSize(orientation);
 }
 
 float ScrollableArea::pixelStep(ScrollbarOrientation) const
 {
     return 1;
 }
 
 } // namespace blink