Remove window.length and window.frames

lib/html/src/CrossFrameTypes.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.
 
 abstract class Window {
   // Fields.
   Location get location;
   History get history;
 
   bool get closed;
   Window get opener;
   Window get parent;
   Window get top;
 
-  // TODO(vsm): Add frames to navigate subframes.  See 2312.
-
   // Methods.
   void focus();
   void blur();
   void close();
   void postMessage(Dynamic message,
                    String targetOrigin,
                    [List messagePorts = null]);
 }
 
 abstract class Location {
   void set href(String val);
 }
 
 abstract class History {
   void back();
   void forward();
   void go(int distance);
 }