Adding tests for experimental Safe DOM creation technique.

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index 968b8ed6c9d854f4073519cf9d1cd982868598d6..0cbb1a704e3fb9a3be240e1ce76058cb95646938 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -17547,6 +17547,16 @@ class Range native "Range" {
   @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