Move PathObserver to mdv_observe package

sdk/lib/mdv_observe_impl/path_observer.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.
 
-part of html;
+part of dart.mdv_observe_impl;
 
 // This code is inspired by ChangeSummary:
 // https://github.com/rafaelw/ChangeSummary/blob/master/change_summary.js
 // ...which underlies MDV. Since we don't need the functionality of
 // ChangeSummary, we just implement what we need for data bindings.
 // This allows our implementation to be much simpler.
 
 // TODO(jmesserly): should we make these types stronger, and require
 // Observable objects? Currently, it is fine to say something like:
 //     var path = new PathObserver(123, '');
@@ skipping 17 matching lines @@
  * `foo.bar.baz`.
  *
  * When the [values] stream is being listened to, this will observe changes to
  * the object and any intermediate object along the path, and send [values]
  * accordingly. When all listeners are unregistered it will stop observing
  * the objects.
  *
  * This class is used to implement [Node.bind] and similar functionality.
  */
 // TODO(jmesserly): find a better home for this type.
-@Experimental
 class PathObserver {
   /** The object being observed. */
   final object;
 
   /** The path string. */
   final String path;
 
   /** True if the path is valid, otherwise false. */
   final bool _isValid;
 
@@ skipping 225 matching lines @@
 
 final _spacesRegExp = new RegExp(r'\s');
 
 bool _isPathValid(String s) {
   s = s.replaceAll(_spacesRegExp, '');
 
   if (s == '') return true;
   if (s[0] == '.') return false;
   return _pathRegExp.hasMatch(s);
 }