Revert initializing formals change in client code

client/observable/observable.dart

 // Copyright (c) 2011, 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.
 
 #library('observable');
 
 #import('dart:coreimpl');
 
 #source('ChangeEvent.dart');
 #source('EventBatch.dart');
@@ skipping 42 matching lines @@
   /** Whether this object is currently observed by listeners or propagators. */
   bool get isObserved() {
     for (Observable obj = this; obj != null; obj = obj.parent) {
       if (listeners.length > 0) {
         return true;
       }
     }
     return false;
   }
 
-  AbstractObservable([Observable parent = null])
-    : this.parent = parent,
-      uid = EventBatch.genUid(),
+  AbstractObservable([Observable this.parent = null])
+    : uid = EventBatch.genUid(),
       listeners = new List<ChangeListener>();
 
   bool addChangeListener(ChangeListener listener) {
     if (listeners.indexOf(listener, 0) == -1) {
       listeners.add(listener);
       return true;
     }
 
     return false;
   }
@@ skipping 214 matching lines @@
     //              equality check should be done?
     if (newValue !== _value) {
       final oldValue = _value;
       _value = newValue;
       recordPropertyUpdate("value", newValue, oldValue);
     }
   }
 
   T _value;
 }