Cache the absolute bounding box rect on RenderLayer.

Source/core/rendering/compositing/RenderLayerCompositor.h

 /*
  * Copyright (C) 2009 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 44 matching lines @@
 // RenderLayerCompositor manages the hierarchy of
 // composited RenderLayers. It determines which RenderLayers
 // become compositing, and creates and maintains a hierarchy of
 // GraphicsLayers based on the RenderLayer painting order.
 //
 // There is one RenderLayerCompositor per RenderView.
 
 class RenderLayerCompositor FINAL : public GraphicsLayerClient {
     WTF_MAKE_FAST_ALLOCATED;
 public:
+    enum BoundsUpdateType {
+        DoNotForceUpdate,
+        ForceUpdate,
+    };
+
     // FIXME: This constructor should take a reference.
     explicit RenderLayerCompositor(RenderView&);
     virtual ~RenderLayerCompositor();
 
     // Return true if this RenderView is in "compositing mode" (i.e. has one or more
     // composited RenderLayers)
     bool inCompositingMode() const { return m_compositing; }
     // This will make a compositing layer at the root automatically, and hook up to
     // the native view/window system.
     void enableCompositingMode(bool enable = true);
@@ skipping 184 matching lines @@
     CompositingReasons subtreeReasonsForCompositing(RenderObject*, bool hasCompositedDescendants, bool has3DTransformedDescendants) const;
 
     // Make or destroy the CompositedLayerMapping for this layer; returns true if the compositedLayerMapping changed.
     bool allocateOrClearCompositedLayerMapping(RenderLayer*, CompositingStateTransitionType compositedLayerUpdate);
     bool updateSquashingAssignment(RenderLayer*, SquashingState&, CompositingStateTransitionType compositedLayerUpdate);
 
     void clearMappingForRenderLayerIncludingDescendants(RenderLayer*);
 
     void recursiveRepaintLayer(RenderLayer*);
 
-    void addToOverlapMap(OverlapMap&, RenderLayer*, IntRect& layerBounds);
+    void addToOverlapMap(OverlapMap&, RenderLayer*, const IntRect& layerBounds);
 
     // Forces an update for all frames of frame tree recursively. Used only when the mainFrame compositor is ready to
     // finish all deferred work.
     static void finishCompositingUpdateForFrameTree(LocalFrame*);
 
     void computeCompositingRequirements(RenderLayer* ancestorLayer, RenderLayer*, OverlapMap*, struct CompositingRecursionData&, bool& descendantHas3DTransform, Vector<RenderLayer*>& unclippedDescendants, IntRect& absoluteDecendantBoundingBox);
 
     // Defines which RenderLayers will paint into which composited backings, by allocating and destroying CompositedLayerMappings as needed.
     void assignLayersToBackings(RenderLayer*, bool& layersChanged);
     void assignLayersToBackingsInternal(RenderLayer*, SquashingState&, bool& layersChanged, RenderLayer* clippingAncestor);
@@ skipping 56 matching lines @@
     CompositingReasonFinder m_compositingReasonFinder;
 
     bool m_hasAcceleratedCompositing;
     bool m_showRepaintCounter;
 
     // FIXME: This should absolutely not be mutable.
     mutable bool m_needsToRecomputeCompositingRequirements;
     bool m_needsToUpdateLayerTreeGeometry;
     GraphicsLayerUpdater::UpdateType m_pendingUpdateType;
 
+    RenderLayerCompositor::BoundsUpdateType m_recomputeLayerBoundsUpdateType;
+
+    bool m_canUseCachedLayerBoundingBoxes;
     bool m_compositing;
     bool m_compositingLayersNeedRebuild;
     bool m_forceCompositingMode;
     bool m_needsUpdateCompositingRequirementsState;
 
     bool m_isTrackingRepaints; // Used for testing.
 
     RootLayerAttachment m_rootLayerAttachment;
 
     // Enclosing container layer, which clips for iframe content
@@ skipping 16 matching lines @@
     OwnPtr<GraphicsLayer> m_layerForScrollCorner;
 #if USE(RUBBER_BANDING)
     OwnPtr<GraphicsLayer> m_layerForOverhangShadow;
 #endif
 };
 
 
 } // namespace WebCore
 
 #endif // RenderLayerCompositor_h