Roll Observatory packages and add a roll script

packages/observe/lib/html.dart

 // Copyright (c) 2013, 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.
 
 // TODO(jmesserly): can we handle this more elegantly?
 // In general, it seems like we want a convenient way to take a Stream plus a
 // getter and convert this into an Observable.
 
 /// Helpers for exposing dart:html as observable data.
 library observe.html;
@@ skipping 59 matching lines @@
     Observable object, String path) {
 
   callback(value) {
     updateCssClass(element, className, value);
   }
 
   var obs = new PathObserver(object, path);
   callback(obs.open(callback));
   return obs;
 }