Fix RenderLayer::collectLayers logic bug.

Source/core/rendering/RenderLayer.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 847 matching lines @@
 
     void setViewportConstrainedNotCompositedReason(ViewportConstrainedNotCompositedReason reason) { m_compositingProperties.viewportConstrainedNotCompositedReason = reason; }
     ViewportConstrainedNotCompositedReason viewportConstrainedNotCompositedReason() const { return static_cast<ViewportConstrainedNotCompositedReason>(m_compositingProperties.viewportConstrainedNotCompositedReason); }
 
     bool isOutOfFlowRenderFlowThread() const { return renderer()->isOutOfFlowRenderFlowThread(); }
 
     enum PaintOrderListType {BeforePromote, AfterPromote};
     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();
 
     bool isStackingContext(const RenderStyle* style) const { return !style->hasAutoZIndex() || isRootLayer(); }
 
     bool isDirtyStackingContainer() const { return m_zOrderListsDirty && isStackingContainer(); }
 
     void setAncestorChainHasSelfPaintingLayerDescendant();
     void dirtyAncestorChainHasSelfPaintingLayerDescendantStatus();
@@ skipping 58 matching lines @@
     void setParent(RenderLayer* parent);
     void setFirstChild(RenderLayer* first) { m_first = first; }
     void setLastChild(RenderLayer* last) { m_last = last; }
 
     LayoutPoint renderBoxLocation() const { return renderer()->isBox() ? toRenderBox(renderer())->location() : LayoutPoint(); }
 
     // layerToForceAsStackingContainer allows us to build pre-promotion and
     // 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)
             : rootLayer(inRootLayer)
             , paintingRoot(inPaintingRoot)
             , paintDirtyRect(inDirtyRect)
             , subPixelAccumulation(inSubPixelAccumulation)
             , region(inRegion)
             , overlapTestRequests(inOverlapTestRequests)
             , paintBehavior(inPaintBehavior)
@@ skipping 62 matching lines @@
         const LayoutRect& hitTestRect, const HitTestLocation&, const HitTestingTransformState* = 0, double* zOffset = 0);
 
     bool listBackgroundIsKnownToBeOpaqueInRect(const Vector<RenderLayer*>*, const LayoutRect&) const;
 
     void computeScrollDimensions();
     bool hasHorizontalOverflow() const;
     bool hasVerticalOverflow() const;
     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;
 
     int scrollPosition(Scrollbar*) const;
     
     // ScrollableArea interface
     virtual void invalidateScrollbarRect(Scrollbar*, const IntRect&);
     virtual void invalidateScrollCornerRect(const IntRect&);
     virtual bool isActive() const;
     virtual bool isScrollCornerVisible() const;
@@ skipping 306 matching lines @@
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const WebCore::RenderLayer*);
 void showLayerTree(const WebCore::RenderObject*);
 #endif
 
 #endif // RenderLayer_h