Make hashCode a getter and not a method.

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 {
   /**
    * Creates a new [Object] instance.
@@ skipping 20 matching lines @@
    *
    * All objects have hash codes. Hash codes are guaranteed to be the
    * same for objects that are equal when compared using the equality
    * operator [:==:]. Other than that there are no guarantees about
    * the hash codes. They will not be consistent between runs and
    * there are no distribution guarantees.
    *
    * If a subclass overrides [hashCode] it should override the
    * equality operator as well to maintain consistency.
    */
-  external int hashCode();
+  external int get hashCode;
 
   /**
    * Returns a string representation of this object.
    */
   external String toString();
 
   /**
    * [noSuchMethod] is invoked when users invoke a non-existant method
    * on an object. The name of the method and the arguments of the
    * invocation are passed to [noSuchMethod]. If [noSuchMethod]
    * returns a value, that value becomes the result of the original
    * invocation.
    *
    * The default behavior of [noSuchMethod] is to throw a
    * [noSuchMethodError].
    */
   external Dynamic noSuchMethod(String name, List args);
   /**
    * A representation of the runtime type of the object.
    */
   external Type get runtimeType;
 }