Do not create scrollbars if the subtree is invisible.

Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1268 matching lines @@
 bool CompositedDeprecatedPaintLayerMapping::toggleScrollbarLayerIfNeeded(OwnPtr<GraphicsLayer>& layer, bool needsLayer, CompositingReasons reason)
 {
     if (needsLayer == !!layer)
         return false;
     layer = needsLayer ? createGraphicsLayer(reason) : nullptr;
     return true;
 }
 
 bool CompositedDeprecatedPaintLayerMapping::updateOverflowControlsLayers(bool needsHorizontalScrollbarLayer, bool needsVerticalScrollbarLayer, bool needsScrollCornerLayer, bool needsAncestorClip)
 {
+    // If the subtree is invisible, we don't actually need scrollbar layers.
+    bool invisible = m_owningLayer.subtreeIsInvisible();
+    needsHorizontalScrollbarLayer &= !invisible;
+    needsVerticalScrollbarLayer &= !invisible;
+    needsScrollCornerLayer &= !invisible;
+
     bool horizontalScrollbarLayerChanged = toggleScrollbarLayerIfNeeded(m_layerForHorizontalScrollbar, needsHorizontalScrollbarLayer, CompositingReasonLayerForHorizontalScrollbar);
     bool verticalScrollbarLayerChanged = toggleScrollbarLayerIfNeeded(m_layerForVerticalScrollbar, needsVerticalScrollbarLayer, CompositingReasonLayerForVerticalScrollbar);
     bool scrollCornerLayerChanged = toggleScrollbarLayerIfNeeded(m_layerForScrollCorner, needsScrollCornerLayer, CompositingReasonLayerForScrollCorner);
 
     bool needsOverflowControlsHostLayer = needsHorizontalScrollbarLayer || needsVerticalScrollbarLayer || needsScrollCornerLayer;
     toggleScrollbarLayerIfNeeded(m_overflowControlsHostLayer, needsOverflowControlsHostLayer, CompositingReasonLayerForOverflowControlsHost);
     bool needsOverflowClipLayer = needsOverflowControlsHostLayer && needsAncestorClip;
     toggleScrollbarLayerIfNeeded(m_overflowControlsClippingLayer, needsOverflowClipLayer, CompositingReasonLayerForOverflowControlsHost);
 
     if (ScrollingCoordinator* scrollingCoordinator = scrollingCoordinatorFromLayer(m_owningLayer)) {
@@ skipping 1064 matching lines @@
     } else if (graphicsLayer == m_scrollingBlockSelectionLayer.get()) {
         name = "Scrolling Block Selection Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink