Optimize the pre-paint tree walk and ClipRects

third_party/WebKit/Source/core/paint/PaintLayer.h

Index: third_party/WebKit/Source/core/paint/PaintLayer.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.h b/third_party/WebKit/Source/core/paint/PaintLayer.h
index 988052902d4b1a9057e26adad6be02955f93750f..fb3c6e80fca416c9738b9ebb6f885aeac137b36f 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -901,11 +901,17 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
     m_previousScrollOffsetAccumulationForPainting = s;
   }
 
-  ClipRects* previousPaintingClipRects() const {
-    return m_previousPaintingClipRects.get();
+  bool hasPreviousPaintingClipRects() const {
+    return m_hasPreviousPaintingClipRects;
   }
-  void setPreviousPaintingClipRects(ClipRects& clipRects) {
-    m_previousPaintingClipRects = &clipRects;
+
+  const ClipRects& previousPaintingClipRects() const {
+    return m_previousPaintingClipRects;
+  }
+
+  void setPreviousPaintingClipRects(const ClipRects& clipRects) {
+    m_previousPaintingClipRects = clipRects;
+    m_hasPreviousPaintingClipRects = true;
   }
 
   LayoutRect previousPaintDirtyRect() const { return m_previousPaintDirtyRect; }
@@ -1200,6 +1206,8 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
 
   unsigned m_selfPaintingStatusChanged : 1;
 
+  unsigned m_hasPreviousPaintingClipRects : 1;
+
   LayoutBoxModelObject& m_layoutObject;
 
   PaintLayer* m_parent;
@@ -1235,7 +1243,7 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
   std::unique_ptr<PaintLayerStackingNode> m_stackingNode;
 
   IntSize m_previousScrollOffsetAccumulationForPainting;
-  RefPtr<ClipRects> m_previousPaintingClipRects;
+  ClipRects m_previousPaintingClipRects;
   LayoutRect m_previousPaintDirtyRect;
 
   std::unique_ptr<PaintLayerRareData> m_rareData;