Adding tests for experimental Safe DOM creation technique.

sdk/lib/html/dart2js/html_dart2js.dart

 /// The Dart HTML library.
 library dart.dom.html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev';
 import 'dart:html_common';
 import 'dart:indexed_db';
 import 'dart:isolate';
 import 'dart:json' as json;
@@ skipping 17529 matching lines @@
   void setStartBefore(Node refNode) native;
 
   @DomName('Range.surroundContents')
   @DocsEditable
   void surroundContents(Node newParent) native;
 
   @DomName('Range.toString')
   @DocsEditable
   String toString() native;
 
+
+  /**
+   * Checks if createContextualFragment is supported.
+   *
+   * See also:
+   *
+   * * [createContextualFragment]
+   */
+  static bool get supportsCreateContextualFragment =>
+      JS('bool', '("createContextualFragment" in window.Range.prototype)');
 }
 // 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.
 
 
 @DocsEditable
 @DomName('RangeException')
 class RangeException native "RangeException" {
 
@@ skipping 11958 matching lines @@
       _position = nextPosition;
       return true;
     }
     _current = null;
     _position = _array.length;
     return false;
   }
 
   T get current => _current;
 }