Reapply conversion of most core interfaces to abstract classes.

lib/coreimpl/duration_implementation.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.
-
-class DurationImplementation implements Duration {
-  final int inMilliseconds;
-
-  const DurationImplementation({int days: 0,
-                                int hours: 0,
-                                int minutes: 0,
-                                int seconds: 0,
-                                int milliseconds: 0})
-    : inMilliseconds = days * Duration.MILLISECONDS_PER_DAY +
-                       hours * Duration.MILLISECONDS_PER_HOUR +
-                       minutes * Duration.MILLISECONDS_PER_MINUTE +
-                       seconds * Duration.MILLISECONDS_PER_SECOND +
-                       milliseconds;
-
-  int get inDays {
-    return inMilliseconds ~/ Duration.MILLISECONDS_PER_DAY;
-  }
-
-  int get inHours {
-    return inMilliseconds ~/ Duration.MILLISECONDS_PER_HOUR;
-  }
-
-  int get inMinutes {
-    return inMilliseconds ~/ Duration.MILLISECONDS_PER_MINUTE;
-  }
-
-  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 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}";
-      return "00${n}";
-    }
-    String twoDigits(int n) {
-      if (n >= 10) return "${n}";
-      return "0${n}";
-    }
-
-    if (inMilliseconds < 0) {
-      Duration duration =
-          new DurationImplementation(milliseconds: -inMilliseconds);
-      return "-${duration}";
-    }
-    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}";
-  }
-}