Preliminary paint property walk implementation for SPv2

third_party/WebKit/Source/core/layout/LayoutObject.h

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index 11c46fa66a0edc82400bce1f6e4c82f9568f487b..d83bcb5ce372d4aefac6b87dacceb4de68db169a 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -60,14 +60,15 @@ class Document;
 class HitTestLocation;
 class HitTestResult;
 class InlineBox;
-class PseudoStyleRequest;
 class LayoutBoxModelObject;
 class LayoutBlock;
 class LayoutFlowThread;
 class LayoutGeometryMap;
-class PaintLayer;
 class LayoutMultiColumnSpannerPlaceholder;
 class LayoutView;
+class ObjectPaintProperties;
+class PaintLayer;
+class PseudoStyleRequest;
 class TransformState;
 
 struct PaintInfo;
@@ -353,6 +354,12 @@ public:
     // Sets the parent of this object but doesn't add it as a child of the parent.
     void setDangerousOneWayParent(LayoutObject*);
 
+    // For SPv2 only. These are implemented as a global hash map temporarily,

[pdr., 2015/10/20 22:02:30]

This is useful but more of an implementation detail. Can you move this comment
to LayoutObject.cpp above the ObjectPaintPropertiesMap typedef?

For readers that hit this, lets use something like the following comment here:
// Paint properties encode the hierarchical transform, clip, scroll, and
// effect information used for painting. Properties should only be changed
// during UpdatePaintProperties, and should only be used during Paint.

[trchen, 2015/10/21 06:16:19]

Done.

+    // to avoid memory regression during the transition towards SPv2.
+    ObjectPaintProperties* objectPaintProperties() const;
+    ObjectPaintProperties& ensureObjectPaintProperties();
+    void clearObjectPaintProperties();
+
 private:
     //////////////////////////////////////////
     // Helper functions. Dangerous to use!