- Add definition of "int hashCode()" to Object.

lib/core/object.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Everything in Dart is an [Object].
  */
 class Object {
   const Object();
 
   bool operator ==(other) => identical(this, other);
 
+  external int hashCode();
+
   external String toString();
 
   external void noSuchMethod(String name, List args);
 
   external Type runtimeType();
 }
 
 abstract class Type {}
 
 /**
  * Check whether two references are to the same object.
  */
 bool identical(Object a, Object b) => a === b;