Track scissored damage area for WebGL

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 364 matching lines @@
         ScrollbarTheme::theme()->updateScrollbarOverlayStyle(scrollbar);
         scrollbar->invalidate();
     }
 }
 
 void ScrollableArea::invalidateScrollbar(Scrollbar* scrollbar, const IntRect& rect)
 {
     if (scrollbar == horizontalScrollbar()) {
         if (GraphicsLayer* graphicsLayer = layerForHorizontalScrollbar()) {
             graphicsLayer->setNeedsDisplay();
-            graphicsLayer->setContentsNeedsDisplay();
+            graphicsLayer->setContentsNeedsDisplay(rect);
             return;
         }
     } else if (scrollbar == verticalScrollbar()) {
         if (GraphicsLayer* graphicsLayer = layerForVerticalScrollbar()) {
             graphicsLayer->setNeedsDisplay();
-            graphicsLayer->setContentsNeedsDisplay();
+            graphicsLayer->setContentsNeedsDisplay(rect);
             return;
         }
     }
     invalidateScrollbarRect(scrollbar, rect);
 }
 
 void ScrollableArea::invalidateScrollCorner(const IntRect& rect)
 {
     if (GraphicsLayer* graphicsLayer = layerForScrollCorner()) {
         graphicsLayer->setNeedsDisplay();
@@ skipping 81 matching lines @@
 {
     return scrollSize(orientation);
 }
 
 float ScrollableArea::pixelStep(ScrollbarOrientation) const
 {
     return 1;
 }
 
 } // namespace blink