[SVGDom] Add <svg> viewBox support

experimental/svg/model/SkSVGRect.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 "SkRect.h"
 #include "SkSVGRect.h"
@@ skipping 40 matching lines @@
             this->setHeight(*h);
         }
         break;
     default:
         this->INHERITED::onSetAttribute(attr, v);
     }
 }
 
 void SkSVGRect::onDraw(SkCanvas* canvas, const SkSVGLengthContext& lctx,
                        const SkPaint& paint) const {
-    const SkRect r = SkRect::MakeXYWH(
-        lctx.resolve(fX, SkSVGLengthContext::LengthType::kHorizontal),
-        lctx.resolve(fY, SkSVGLengthContext::LengthType::kVertical),
-        lctx.resolve(fWidth, SkSVGLengthContext::LengthType::kHorizontal),
-        lctx.resolve(fHeight, SkSVGLengthContext::LengthType::kVertical));
-
-    canvas->drawRect(r, paint);
+    canvas->drawRect(lctx.resolveRect(fX, fY, fWidth, fHeight), paint);
 }