Make hashCode a getter and not a method.

lib/coreimpl/date.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.
 
 class DateImplementation implements Date {
   final int millisecondsSinceEpoch;
   final bool isUtc;
 
   factory DateImplementation.fromString(String formattedString) {
     // Read in (a subset of) ISO 8601.
@@ skipping 72 matching lines @@
 
   bool operator >(Date other)
       => millisecondsSinceEpoch > other.millisecondsSinceEpoch;
 
   bool operator >=(Date other)
       => millisecondsSinceEpoch >= other.millisecondsSinceEpoch;
 
   int compareTo(Date other)
       => millisecondsSinceEpoch.compareTo(other.millisecondsSinceEpoch);
 
-  int hashCode() => millisecondsSinceEpoch;
+  int get hashCode => millisecondsSinceEpoch;
 
   Date toLocal() {
     if (isUtc) {
       return new Date.fromMillisecondsSinceEpoch(millisecondsSinceEpoch,
                                                  isUtc: false);
     }
     return this;
   }
 
   Date toUtc() {
@@ skipping 74 matching lines @@
   external Duration get timeZoneOffset;
   external int get year;
   external int get month;
   external int get day;
   external int get hour;
   external int get minute;
   external int get second;
   external int get millisecond;
   external int get weekday;
 }