[SVGDom] Add opacity support

experimental/svg/model/SkSVGAttribute.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 SkSVGAttribute_DEFINED
 #define SkSVGAttribute_DEFINED
 
 #include "SkSVGTypes.h"
 #include "SkTLazy.h"
 
 class SkSVGRenderContext;
 
 enum class SkSVGAttribute {
     kD,
     kFill,
     kFillOpacity,
     kHeight,
+    kOpacity,
     kPoints,
     kRx,
     kRy,
     kStroke,
     kStrokeOpacity,
     kStrokeLineCap,
     kStrokeLineJoin,
     kStrokeWidth,
     kTransform,
     kViewBox,
@@ skipping 10 matching lines @@
     // TODO: SkTLazy adds an extra ptr per attribute; refactor to reduce overhead.
 
     SkTLazy<SkSVGPaint>      fFill;
     SkTLazy<SkSVGNumberType> fFillOpacity;
 
     SkTLazy<SkSVGPaint>      fStroke;
     SkTLazy<SkSVGLineCap>    fStrokeLineCap;
     SkTLazy<SkSVGLineJoin>   fStrokeLineJoin;
     SkTLazy<SkSVGNumberType> fStrokeOpacity;
     SkTLazy<SkSVGLength>     fStrokeWidth;
+
+    SkTLazy<SkSVGNumberType> fOpacity;
 };
 
 #endif // SkSVGAttribute_DEFINED