[SVGDom] Initial linear gradient support

experimental/svg/model/SkSVGNode.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 SkSVGNode_DEFINED
 #define SkSVGNode_DEFINED
 
 #include "SkRefCnt.h"
 #include "SkSVGAttribute.h"
 
 class SkCanvas;
 class SkMatrix;
+class SkPaint;
 class SkSVGRenderContext;
 class SkSVGValue;
 
 enum class SkSVGTag {
     kCircle,
+    kDefs,
     kEllipse,
     kG,
     kLine,
+    kLinearGradient,
     kPath,
     kPolygon,
     kPolyline,
     kRect,
+    kStop,
     kSvg
 };
 
 class SkSVGNode : public SkRefCnt {
 public:
     virtual ~SkSVGNode();
 
     SkSVGTag tag() const { return fTag; }
 
     virtual void appendChild(sk_sp<SkSVGNode>) = 0;
 
     void render(const SkSVGRenderContext&) const;
+    bool asPaint(const SkSVGRenderContext&, SkPaint*) const;
 
     void setAttribute(SkSVGAttribute, const SkSVGValue&);
 
     void setFill(const SkSVGPaint&);
     void setFillOpacity(const SkSVGNumberType&);
     void setOpacity(const SkSVGNumberType&);
     void setStroke(const SkSVGPaint&);
     void setStrokeOpacity(const SkSVGNumberType&);
     void setStrokeWidth(const SkSVGLength&);
 
 protected:
     SkSVGNode(SkSVGTag);
 
     // Called before onRender(), to apply local attributes to the context.  Unlike onRender(),
     // onPrepareToRender() bubbles up the inheritance chain: overriders should always call
     // INHERITED::onPrepareToRender(), unless they intend to short-circuit rendering
     // (return false).
     // Implementations are expected to return true if rendering is to continue, or false if
     // the node/subtree rendering is disabled.
     virtual bool onPrepareToRender(SkSVGRenderContext*) const;
 
     virtual void onRender(const SkSVGRenderContext&) const = 0;
 
+    virtual bool onAsPaint(const SkSVGRenderContext&, SkPaint*) const { return false; }
+
     virtual void onSetAttribute(SkSVGAttribute, const SkSVGValue&);
 
 private:
     SkSVGTag                    fTag;
 
     // FIXME: this should be sparse
     SkSVGPresentationAttributes fPresentationAttributes;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif // SkSVGNode_DEFINED