Add Selection.toString() calling the native method

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index e4f8fe3bbcde259a7de30d6ab31fc4cc0df15c7d..3834cccb7cebede1404e11ac52e3a3cefca4f3a9 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -32853,14 +32853,13 @@ class SelectElement extends HtmlElement {
     }
   }
 }
-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2017, 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.
 
 
-@DocsEditable()
 @DomName('Selection')
 class Selection extends DartHtmlDomObject {
   // To suppress missing implicit constructor warnings.