fix PathObserver to avoid try+catch

pkg/observe/lib/src/change_record.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;
+library observe.src.change_record;
+
+import 'package:observe/observe.dart';
+
 
 /** Records a change to an [Observable]. */
 // TODO(jmesserly): remove this type
 abstract class ChangeRecord {}
 
 /** A change record to a field of an observable object. */
 class PropertyChangeRecord<T> extends ChangeRecord {
-  /**
-   * *Deprecated* use [name] instead.
-   * The field that was changed.
-   */
-  @deprecated
-  Symbol get field => name;
-
   /** The object that changed. */
   final object;
 
   /** The name of the property that changed. */
   final Symbol name;
 
   /** The previous value of the property. */
   final T oldValue;
 
   /** The new value of the property. */
   final T newValue;
 
   PropertyChangeRecord(this.object, this.name, this.oldValue, this.newValue);
 
-  /*
-   * *Deprecated* instead of `record.changes(key)` simply do
-   * `key == record.name`.
-   */
-  @deprecated
-  bool changes(key) => key is Symbol && name == key;
-
   String toString() =>
       '#<PropertyChangeRecord $name from: $oldValue to: $newValue>';
 }
 
 /** A change record for an observable list. */
 class ListChangeRecord extends ChangeRecord {
   /** The starting index of the change. */
   final int index;
 
   /** The number of items removed. */
   final int removedCount;
 
   /** The number of items added. */
   final int addedCount;
 
   ListChangeRecord(this.index, {this.removedCount: 0, this.addedCount: 0}) {
     if (addedCount == 0 && removedCount == 0) {
       throw new ArgumentError('added and removed counts should not both be '
           'zero. Use 1 if this was a single item update.');
     }
   }
 
-  /**
-   * *Deprecated* use [indexChanged] instead.
-   * Returns true if the provided index was changed by this operation.
-   */
-  @deprecated
-  bool changes(value) => indexChanged(value);
-
   /** Returns true if the provided index was changed by this operation. */
   bool indexChanged(otherIndex) {
     // If key isn't an int, or before the index, then it wasn't changed.
     if (otherIndex is! int || otherIndex < index) return false;
 
     // If this was a shift operation, anything after index is changed.
     if (addedCount != removedCount) return true;
 
     // Otherwise, anything in the update range was changed.
     return otherIndex < index + addedCount;
   }
 
   String toString() => '#<ListChangeRecord index: $index, '
       'removed: $removedCount, addedCount: $addedCount>';
 }