Change Future.delayed to take a Duration.

sdk/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.
 
 part of dart.core;
 
 /**
  * A [Duration] represents a time span. A duration can be negative.
  */
 class Duration implements Comparable {
   static const int MILLISECONDS_PER_SECOND = 1000;
   static const int SECONDS_PER_MINUTE = 60;
   static const int MINUTES_PER_HOUR = 60;
   static const int HOURS_PER_DAY = 24;
 
   static const int MILLISECONDS_PER_MINUTE =
       MILLISECONDS_PER_SECOND * SECONDS_PER_MINUTE;
   static const int MILLISECONDS_PER_HOUR =
       MILLISECONDS_PER_MINUTE * MINUTES_PER_HOUR;
   static const int MILLISECONDS_PER_DAY =
       MILLISECONDS_PER_HOUR * HOURS_PER_DAY;
 
   static const int SECONDS_PER_HOUR = SECONDS_PER_MINUTE * MINUTES_PER_HOUR;
   static const int SECONDS_PER_DAY = SECONDS_PER_HOUR * HOURS_PER_DAY;
 
   static const int MINUTES_PER_DAY = MINUTES_PER_HOUR * HOURS_PER_DAY;
 
+  static const Duration ZERO = const Duration(seconds: 0);
+
   /**
    * This [Duration] in milliseconds.
    */
   final int inMilliseconds;
 
   /**
    * The duration is the sum of all individual parts. This means that individual
    * parts don't need to be less than the next-bigger unit. For example [hours]
    * is allowed to have a value greater than 23.
    *
@@ skipping 119 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";
   }
 }