Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGPolygonElement.dart

Index: lib/html/doc/interface/SVGPolygonElement.dart
diff --git a/lib/html/doc/interface/SVGPolygonElement.dart b/lib/html/doc/interface/SVGPolygonElement.dart
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index 0000000000000000000000000000000000000000..330a0f7c63425757e2ba309b8b885d54f9152b8b
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+++ b/lib/html/doc/interface/SVGPolygonElement.dart
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+// 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.
+
+// WARNING: Do not edit - generated code.
+
+/// @domName SVGPolygonElement
+interface SVGPolygonElement extends SVGElement, SVGTests, SVGLangSpace, SVGExternalResourcesRequired, SVGStylable, SVGTransformable {
+
+  /** @domName SVGPolygonElement.animatedPoints */
+  final SVGPointList animatedPoints;
+
+  /** @domName SVGPolygonElement.points */
+  final SVGPointList points;
+}