[SVGDom] Add opacity support

experimental/svg/model/SkSVGRenderContext.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvas.h"
 #include "SkSVGAttribute.h"
 #include "SkSVGRenderContext.h"
@@ skipping 206 matching lines @@
 
     ApplyLazyInheritedAttribute(Fill);
     ApplyLazyInheritedAttribute(FillOpacity);
     ApplyLazyInheritedAttribute(Stroke);
     ApplyLazyInheritedAttribute(StrokeLineCap);
     ApplyLazyInheritedAttribute(StrokeLineJoin);
     ApplyLazyInheritedAttribute(StrokeOpacity);
     ApplyLazyInheritedAttribute(StrokeWidth);
 
 #undef ApplyLazyInheritedAttribute
+
+    // Uninherited attributes.  Only apply to the current context.
+
+    if (auto* opacity = attrs.fOpacity.getMaybeNull()) {
+        SkPaint opacityPaint;
+        opacityPaint.setAlpha(static_cast<uint8_t>(opacity->value() * 255));
+        // Balanced in the destructor, via restoreToCount().
+        fCanvas->saveLayer(nullptr, &opacityPaint);
+    }
 }
 
 const SkPaint* SkSVGRenderContext::fillPaint() const {
     const SkSVGPaint::Type paintType = fPresentationContext->fInherited.fFill.get()->type();
     return paintType != SkSVGPaint::Type::kNone ? &fPresentationContext->fFillPaint : nullptr;
 }
 
 const SkPaint* SkSVGRenderContext::strokePaint() const {
     const SkSVGPaint::Type paintType = fPresentationContext->fInherited.fStroke.get()->type();
     return paintType != SkSVGPaint::Type::kNone ? &fPresentationContext->fStrokePaint : nullptr;
 }