Make hashCode a getter and not a method.

lib/core/duration.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.
 
 // Dart core library.
 
 /**
  * A [Duration] represents a time span. A duration can be negative.
  */
 class Duration implements Comparable {
@@ skipping 67 matching lines @@
    */
   int get inSeconds {
     return inMilliseconds ~/ Duration.MILLISECONDS_PER_SECOND;
   }
 
   bool operator ==(other) {
     if (other is !Duration) return false;
     return inMilliseconds == other.inMilliseconds;
   }
 
-  int hashCode() {
-    return inMilliseconds.hashCode();
+  int get hashCode {
+    return inMilliseconds.hashCode;
   }
 
   int compareTo(Duration other) {
     return inMilliseconds.compareTo(other.inMilliseconds);
   }
 
   String toString() {
     String threeDigits(int n) {
       if (n >= 100) return "$n";
       if (n > 10) return "0$n";
@@ skipping 11 matching lines @@
     }
     String twoDigitMinutes =
         twoDigits(inMinutes.remainder(Duration.MINUTES_PER_HOUR));
     String twoDigitSeconds =
         twoDigits(inSeconds.remainder(Duration.SECONDS_PER_MINUTE));
     String threeDigitMs =
         threeDigits(inMilliseconds.remainder(Duration.MILLISECONDS_PER_SECOND));
     return "$inHours:$twoDigitMinutes:$twoDigitSeconds.$threeDigitMs";
   }
 }