Clean up the way layout tests force elements to opt in/out of composited scrolling.

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 849 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> >&);
 
+    enum ForceNeedsCompositedScrollingMode {
+        DoNotForceCompositedScrolling = 0,
+        CompositedScrollingAlwaysOn = 1,
+        CompositedScrollingAlwaysOff = 2
+    };
+    void setForceNeedsCompositedScrolling(ForceNeedsCompositedScrollingMode);
+
 private:
     enum CollectLayersBehavior { StopAtStackingContexts, StopAtStackingContainers };
 
     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 clearZOrderLists();
 
     void updateNormalFlowList();
@@ skipping 27 matching lines @@
     void updateStackingContextsAfterStyleChange(const RenderStyle* oldStyle);
 
     void updateScrollbarsAfterStyleChange(const RenderStyle* oldStyle);
     void updateScrollbarsAfterLayout();
 
     void setAncestorChainHasOutOfFlowPositionedDescendant(RenderObject* containingBlock);
     void dirtyAncestorChainHasOutOfFlowPositionedDescendantStatus();
     void updateOutOfFlowPositioned(const RenderStyle* oldStyle);
 
     void updateNeedsCompositedScrolling();
+    void didUpdateNeedsCompositedScrolling();
 
     // Returns true if the position changed.
     bool updateLayerPosition();
 
     void updateLayerPositions(RenderGeometryMap* = 0, UpdateLayerPositionsFlags = defaultFlags);
 
     enum UpdateLayerPositionsAfterScrollFlag {
         NoFlag = 0,
         IsOverflowScroll = 1 << 0,
         HasSeenViewportConstrainedAncestor = 1 << 1,
@@ skipping 364 matching lines @@
 
         // The reason, if any exists, that a fixed-position layer is chosen not to be composited.
         unsigned viewportConstrainedNotCompositedReason : 2;
 
         // Once computed, indicates all that a layer needs to become composited using the CompositingReasons enum bitfield.
         CompositingReasons compositingReasons;
     };
 
     CompositingProperties m_compositingProperties;
 
+    ForceNeedsCompositedScrollingMode m_forceNeedsCompositedScrolling;
+
 private:
     IntRect m_blockSelectionGapsBounds;
 
     OwnPtr<RenderLayerBacking> m_backing;
 };
 
 inline void RenderLayer::clearZOrderLists()
 {
     ASSERT(!isStackingContainer());
 
@@ skipping 39 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