Add dummy dart:html library for documentation.

lib/html/doc/interface/SVGTests.dart

+// 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 SVGTests
+interface SVGTests {
+
+  /** @domName SVGTests.requiredExtensions */
+  final SVGStringList requiredExtensions;
+
+  /** @domName SVGTests.requiredFeatures */
+  final SVGStringList requiredFeatures;
+
+  /** @domName SVGTests.systemLanguage */
+  final SVGStringList systemLanguage;
+
+  /** @domName SVGTests.hasExtension */
+  bool hasExtension(String extension);
+}