Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGElement.dartdoc

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @domName SVGElement
+interface SVGElement extends Element default _SVGElementFactoryProvider {
+
+  SVGElement.tag(String tag);
+  SVGElement.svg(String svg);
+
+  SVGElement clone(bool deep);
+
+
+  /** @domName SVGElement.id */
+  String id;
+
+  /** @domName SVGElement.ownerSVGElement */
+  final SVGSVGElement ownerSVGElement;
+
+  /** @domName SVGElement.viewportElement */
+  final SVGElement viewportElement;
+
+  /** @domName SVGElement.xmlbase */
+  String xmlbase;
+
+}