Move PathObserver to mdv_observe package

sdk/lib/mdv_observe_impl/mdv_observe_impl.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.
 
 // This library itself is undocumented and not supported for end use.
 // Because dart:html must use some of this functionality, it has to be available
 // via a dart:* library. The public APIs are reexported via package:mdv_observe.
 // Generally we try to keep this library minimal, with utility types and
 // functions in the package.
 library dart.mdv_observe_impl;
 
 import 'dart:async';
 import 'dart:collection';
 
+part 'path_observer.dart';
+
 /**
  * Interface representing an observable object. This is used by data in
  * model-view architectures to notify interested parties of [changes].
  *
  * This object does not require any specific technique to implement
  * observability.
  *
  * You can use [ObservableMixin] as a base class or mixin to implement this.
  */
 abstract class Observable {
@@ skipping 192 matching lines @@
 /** Queues an action to happen during the [deliverChangeRecords] timeslice. */
 void queueChangeRecords(void deliverChanges()) {
   if (_deliverCallbacks == null) {
     _deliverCallbacks = new Queue<Function>();
     runAsync(deliverChangeRecords);
   }
   _deliverCallbacks.add(deliverChanges);
 }
 
 Queue _deliverCallbacks;