[S.P.] Use 'const LayoutObject&' in SVGMaskPainter.

Source/core/paint/SVGMaskPainter.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 SVGMaskPainter_h
 #define SVGMaskPainter_h
 
 #include "platform/geometry/FloatRect.h"
 #include "platform/graphics/paint/DisplayItem.h"
 
 namespace blink {
 
 class GraphicsContext;
 class LayoutObject;
 class LayoutSVGResourceMasker;
 
 class SVGMaskPainter {
 public:
     SVGMaskPainter(LayoutSVGResourceMasker& mask) : m_mask(mask) { }
 
-    bool prepareEffect(LayoutObject*, GraphicsContext*);
-    void finishEffect(LayoutObject*, GraphicsContext*);
+    bool prepareEffect(const LayoutObject&, GraphicsContext*);
+    void finishEffect(const LayoutObject&, GraphicsContext*);
 
 private:
     void drawMaskForRenderer(GraphicsContext*, DisplayItemClient, const FloatRect& targetBoundingBox);
 
     LayoutSVGResourceMasker& m_mask;
 };
 
 } // namespace blink
 
 #endif // SVGMaskPainter_h