Reland of duce copying of local data structures in GeometryMapper and PaintLayerClipper.

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

Index: third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h
diff --git a/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h
index 634292466820fdcb00809a6b1e83e483e73c4e1a..b2ea1131d758d312a605e0b8a973344ace231178 100644
--- a/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h
+++ b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h
@@ -34,15 +34,16 @@
   void invalidatePaintLayerOptimizationsIfNeeded(const LayoutObject&,
                                                  PrePaintTreeWalkContext&);
 
-  // Returns the clip applied to children for the given
+  // Returns in |clipRect| the clip applied to children for the given
   // contaiing block context + effect, in the space of ancestorState adjusted
   // by ancestorPaintOffset. Sets hasClip to true if a clip was applied.
-  FloatClipRect clipRectForContext(
+  void computeClipRectForContext(
       const PaintPropertyTreeBuilderContext::ContainingBlockContext&,
       const EffectPaintPropertyNode*,
       const PropertyTreeState& ancestorState,
       const LayoutPoint& ancestorPaintOffset,
-      bool& hasClip);
+      bool& hasClip,
+      FloatClipRect&);
 
   // Returns true if the tree walk should stop before processing this object.
   bool shouldEndWalkBefore(const LayoutObject&, const PrePaintTreeWalkContext&);