package:observe fix various api issues

pkg/observe/lib/src/bind_property.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 observe;
 
 /**
  * Forwards an observable property from one object to another. For example:
  *
- *     class MyModel extends ObservableBase {
+ *     class MyModel extends Observable {
  *       StreamSubscription _sub;
  *       MyOtherModel _otherModel;
  *
  *       MyModel() {
  *         ...
  *         _sub = onPropertyChange(_otherModel, #value,
  *             () => notifyProperty(this, #prop);
  *       }
  *
  *       String get prop => _otherModel.value;
  *       set prop(String value) { _otherModel.value = value; }
  *     }
  *
  * See also [notifyProperty].
  */
 // TODO(jmesserly): make this an instance method?
 StreamSubscription onPropertyChange(Observable source, Symbol sourceName,
     void callback()) {
   return source.changes.listen((records) {
     for (var record in records) {
-      if (record.changes(sourceName)) {
+      if (record is PropertyChangeRecord &&
+          (record as PropertyChangeRecord).name == sourceName) {
         callback();
+        break;
       }
     }
   });
 }