Non-composited scrolling div should invalidate when it has descendant paints to its backing

Source/core/rendering/compositing/CompositedLayerMapping.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 143 matching lines @@
     if (!page)
         return 0;
 
     return page->scrollingCoordinator();
 }
 
 CompositedLayerMapping::CompositedLayerMapping(RenderLayer& layer)
     : m_owningLayer(layer)
     , m_pendingUpdateScope(GraphicsLayerUpdateNone)
     , m_isMainFrameRenderViewLayer(false)
-    , m_requiresOwnBackingStoreForIntrinsicReasons(true)
-    , m_requiresOwnBackingStoreForAncestorReasons(true)
+    , m_requiresOwnBackingStoreForIntrinsicReasons(false)
+    , m_requiresOwnBackingStoreForAncestorReasons(false)

[abarth-chromium, 2014/08/14 03:54:54]

This CL seems fine to me, but we should get vollick's opinion about this part of
the change.

By way of context, we're hoping to eventually remove
HasOwnBackingButPaintsIntoAncestor once some work lands in CC.

[Ian Vollick, 2014/08/14 17:16:44]

This seems fine to me. Using dirty bits here feels like overkill.

     , m_backgroundLayerPaintsFixedRootBackground(false)
     , m_scrollingContentsAreEmpty(false)
 {
     if (layer.isRootLayer() && renderer()->frame()->isMainFrame())
         m_isMainFrameRenderViewLayer = true;
 
     createPrimaryGraphicsLayer();
 }
 
 CompositedLayerMapping::~CompositedLayerMapping()
@@ skipping 2111 matching lines @@
     } else if (graphicsLayer == m_scrollingBlockSelectionLayer.get()) {
         name = "Scrolling Block Selection Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink