[SVGDom] Opacity optimization

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
 
@@ skipping 51 matching lines @@
     // 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&);
 
+    virtual bool hasChildren() const { return false; }
+
 private:
     SkSVGTag                    fTag;
 
     // FIXME: this should be sparse
     SkSVGPresentationAttributes fPresentationAttributes;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif // SkSVGNode_DEFINED