Track scissored damage area for WebGL

Source/platform/scroll/ScrollableArea.cpp

Index: Source/platform/scroll/ScrollableArea.cpp
diff --git a/Source/platform/scroll/ScrollableArea.cpp b/Source/platform/scroll/ScrollableArea.cpp
index f1704953f0a5b59e98c1fe0d1817a5658c6be6a6..4ce26648d4c094fef5eb1afe2ef2783ef745b81f 100644
--- a/Source/platform/scroll/ScrollableArea.cpp
+++ b/Source/platform/scroll/ScrollableArea.cpp
@@ -382,13 +382,13 @@ void ScrollableArea::invalidateScrollbar(Scrollbar* scrollbar, const IntRect& re
     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;
         }
     }