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

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PrePaintTreeWalk_h
 #define PrePaintTreeWalk_h
 
 #include "core/paint/ClipRect.h"
 #include "core/paint/PaintInvalidator.h"
 #include "core/paint/PaintPropertyTreeBuilder.h"
@@ skipping 16 matching lines @@
 
  private:
   void walk(FrameView&, const PrePaintTreeWalkContext&);
   void walk(const LayoutObject&, const PrePaintTreeWalkContext&);
 
   // Invalidates paint-layer painting optimizations, such as subsequence caching
   // and empty paint phase optimizations if clips from the context have changed.
   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&);
 
   PaintPropertyTreeBuilder m_propertyTreeBuilder;
   PaintInvalidator m_paintInvalidator;
   GeometryMapper& m_geometryMapper;
 };
 
 }  // namespace blink
 
 #endif  // PrePaintTreeWalk_h