Fix RenderLayer::collectLayers logic bug.

Source/core/rendering/RenderLayer.h

Index: Source/core/rendering/RenderLayer.h
diff --git a/Source/core/rendering/RenderLayer.h b/Source/core/rendering/RenderLayer.h
index b7f096f270f86d10aaa37e88d839f7b094508e71..f139ff89bd9b089f4476ee025915c2a8adc5ae83 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -865,12 +865,16 @@ public:
     void computePaintOrderList(PaintOrderListType type, Vector<RefPtr<Node> >&);
 
 private:
-    enum CollectLayersBehavior { StopAtStackingContexts, StopAtStackingContainers };
+enum CollectLayersBehavior {
+    ForceLayerToStackingContainer,
+    OverflowScrollCanBeStackingContainers,
+    OnlyStackingContextsCanBeStackingContainers
+};
 
     void updateZOrderLists();
     void rebuildZOrderLists();
     // See the comment for collectLayers for information about the layerToForceAsStackingContainer parameter.
-    void rebuildZOrderLists(CollectLayersBehavior, OwnPtr<Vector<RenderLayer*> >&, OwnPtr<Vector<RenderLayer*> >&, const RenderLayer* layerToForceAsStackingContainer = 0);
+    void rebuildZOrderLists(OwnPtr<Vector<RenderLayer*> >&, OwnPtr<Vector<RenderLayer*> >&, const RenderLayer* layerToForceAsStackingContainer = 0, CollectLayersBehavior = OverflowScrollCanBeStackingContainers);
     void clearZOrderLists();
 
     void updateNormalFlowList();
@@ -949,7 +953,7 @@ private:
     // post-promotion layer lists, by allowing us to treat a layer as if it is a
     // stacking context, without adding a new member to RenderLayer or modifying
     // the style (which could cause extra allocations).
-    void collectLayers(bool includeHiddenLayers, CollectLayersBehavior, OwnPtr<Vector<RenderLayer*> >&, OwnPtr<Vector<RenderLayer*> >&, const RenderLayer* layerToForceAsStackingContainer = 0);
+    void collectLayers(bool includeHiddenLayers, OwnPtr<Vector<RenderLayer*> >&, OwnPtr<Vector<RenderLayer*> >&, const RenderLayer* layerToForceAsStackingContainer = 0, CollectLayersBehavior = OverflowScrollCanBeStackingContainers);
 
     struct LayerPaintingInfo {
         LayerPaintingInfo(RenderLayer* inRootLayer, const LayoutRect& inDirtyRect, PaintBehavior inPaintBehavior, const LayoutSize& inSubPixelAccumulation, RenderObject* inPaintingRoot = 0, RenderRegion*inRegion = 0, OverlapTestRequestMap* inOverlapTestRequests = 0)
@@ -1032,7 +1036,7 @@ private:
     bool hasScrollableHorizontalOverflow() const;
     bool hasScrollableVerticalOverflow() const;
 
-    bool shouldBeNormalFlowOnly() const;
+    bool shouldBeNormalFlowOnly(bool canNeedCompositedScrolling = true) const;

[Julien - ping for review, 2013/05/30 22:23:07]

Really not a huge fan of adding a default *boolean* argument to this function,
especially since its function is unclear to most people.

Could we just split the 2 call paths between the one that doesn't require
needsCompositedScrolling() and the other one?

[hartmanng, 2013/05/31 13:55:41]

Done.

 
     bool shouldBeSelfPaintingLayer() const;