[SVGDom] Add <svg> viewBox support

experimental/svg/model/SkSVGSVG.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 SkSVGSVG_DEFINED
 #define SkSVGSVG_DEFINED
 
 #include "SkSVGContainer.h"
 #include "SkSVGTypes.h"
+#include "SkTLazy.h"
 
 class SkSVGSVG : public SkSVGContainer {
 public:
     virtual ~SkSVGSVG() = default;
 
     static sk_sp<SkSVGSVG> Make() { return sk_sp<SkSVGSVG>(new SkSVGSVG()); }
 
     void setX(const SkSVGLength&);
     void setY(const SkSVGLength&);
     void setWidth(const SkSVGLength&);
     void setHeight(const SkSVGLength&);
+    void setViewBox(const SkSVGViewBoxType&);
 
 protected:
+    bool onPrepareToRender(SkSVGRenderContext*) const override;
+
     void onSetAttribute(SkSVGAttribute, const SkSVGValue&) override;
 
 private:
     SkSVGSVG();
 
     SkSVGLength fX      = SkSVGLength(0);
     SkSVGLength fY      = SkSVGLength(0);
     SkSVGLength fWidth  = SkSVGLength(100, SkSVGLength::Unit::kPercentage);
     SkSVGLength fHeight = SkSVGLength(100, SkSVGLength::Unit::kPercentage);
 
+    SkTLazy<SkSVGViewBoxType> fViewBox;
+
     typedef SkSVGContainer INHERITED;
 };
 
 #endif // SkSVGSVG_DEFINED