fix PathObserver to avoid try+catch

pkg/observe/lib/src/change_record.dart

Index: pkg/observe/lib/src/change_record.dart
diff --git a/pkg/observe/lib/src/change_record.dart b/pkg/observe/lib/src/change_record.dart
index bb584e8f427aa2e35f0e9dc612a774094e0c21c8..39e5964b6d7fd9e1e2010b3f243e790c556f6e9b 100644
--- a/pkg/observe/lib/src/change_record.dart
+++ b/pkg/observe/lib/src/change_record.dart
@@ -2,7 +2,10 @@
 // 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
@@ -10,13 +13,6 @@ 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;
 
@@ -31,13 +27,6 @@ class PropertyChangeRecord<T> extends ChangeRecord {
 
   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>';
 }
@@ -60,13 +49,6 @@ class ListChangeRecord extends ChangeRecord {
     }
   }
 
-  /**
-   * *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.