[SVGDom] Add <svg> viewBox support

experimental/svg/model/SkSVGShape.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkSVGShape_DEFINED
 #define SkSVGShape_DEFINED
 
 #include "SkSVGTransformableNode.h"
 
 class SkSVGLengthContext;
 class SkPaint;
 
 class SkSVGShape : public SkSVGTransformableNode {
 public:
     virtual ~SkSVGShape() = default;
 
     void appendChild(sk_sp<SkSVGNode>) override;
 
 protected:
     SkSVGShape(SkSVGTag);
 
-    void onRender(SkCanvas*, const SkSVGRenderContext&) const final;
+    void onRender(const SkSVGRenderContext&) const final;
 
     virtual void onDraw(SkCanvas*, const SkSVGLengthContext&, const SkPaint&) const = 0;
 
 private:
     typedef SkSVGTransformableNode INHERITED;
 };
 
 #endif // SkSVGShape_DEFINED