[SVGDom] SVGPong sample app

experimental/svg/model/SkSVGDOM.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 "SkDOM.h"
 #include "SkParsePath.h"
@@ skipping 321 matching lines @@
                                SkSVGLengthContext(fContainerSize),
                                SkSVGPresentationContext());
         fRoot->render(ctx);
     }
 }
 
 void SkSVGDOM::setContainerSize(const SkSize& containerSize) {
     // TODO: inval
     fContainerSize = containerSize;
 }
+
+void SkSVGDOM::setRoot(sk_sp<SkSVGNode> root) {
+    fRoot = std::move(root);
+}