[SVGDom] Add <svg> viewBox support

experimental/svg/model/SkSVGShape.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 "SkSVGRenderContext.h"
 #include "SkSVGShape.h"
 
 SkSVGShape::SkSVGShape(SkSVGTag t) : INHERITED(t) {}
 
-void SkSVGShape::onRender(SkCanvas* canvas, const SkSVGRenderContext& ctx) const {
-    if (const SkPaint* fillPaint = ctx.fillPaint()) {
-        this->onDraw(canvas, ctx.lengthContext(), *fillPaint);
+void SkSVGShape::onRender(const SkSVGRenderContext& ctx) const {
+    if (const SkPaint* fillPaint = ctx.presentationContext().fillPaint()) {
+        this->onDraw(ctx.canvas(), ctx.lengthContext(), *fillPaint);
     }
 
-    if (const SkPaint* strokePaint = ctx.strokePaint()) {
-        this->onDraw(canvas, ctx.lengthContext(), *strokePaint);
+    if (const SkPaint* strokePaint = ctx.presentationContext().strokePaint()) {
+        this->onDraw(ctx.canvas(), ctx.lengthContext(), *strokePaint);
     }
 }
 
 void SkSVGShape::appendChild(sk_sp<SkSVGNode>) {
     SkDebugf("cannot append child nodes to an SVG shape.\n");
 }