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

Source/core/rendering/compositing/CompositedLayerMapping.cpp

Index: Source/core/rendering/compositing/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/compositing/CompositedLayerMapping.cpp b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
index 9e3335ed6deed3fccde6340ddb091513eddf8b8b..647e62146c4e1a9deca933da8a75d1e533e85132 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
@@ -161,8 +161,8 @@ 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)
 {