Convert most interfaces in dart:core to abstract classes.

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 44 matching lines @@
       if (addOneMillisecond) millisecondsSinceEpoch++;
       return new Date.fromMillisecondsSinceEpoch(millisecondsSinceEpoch, isUtc);
     } else {
       throw new IllegalArgumentException(formattedString);
     }
   }
 
   static const int _MAX_MILLISECONDS_SINCE_EPOCH = 8640000000000000;
 
   DateImplementation.fromMillisecondsSinceEpoch(this.millisecondsSinceEpoch,
-                                                [this.isUtc = false]) {
+                                                this.isUtc) {
     if (millisecondsSinceEpoch.abs() > _MAX_MILLISECONDS_SINCE_EPOCH) {
       throw new IllegalArgumentException(millisecondsSinceEpoch);
     }
     if (isUtc === null) throw new IllegalArgumentException(isUtc);
   }
 
   bool operator ==(other) {
     if (!(other is Date)) return false;
     return (millisecondsSinceEpoch == other.millisecondsSinceEpoch);
   }
@@ skipping 76 matching lines @@
         ms - duration.inMilliseconds, isUtc);
   }
 
   /** Returns a [Duration] with the difference of [this] and [other]. */
   Duration difference(Date other) {
     int ms = millisecondsSinceEpoch;
     int otherMs = other.millisecondsSinceEpoch;
     return new Duration(milliseconds: ms - otherMs);
   }
 
+  // TODO(lrn): Make parameters not optional for the implementation class.
   external DateImplementation(int year,
-                              [int month,
-                               int day,
-                               int hour,
-                               int minute,
-                               int second,
-                               int millisecond,
-                               bool isUtc]);
+                              [int month = 1,
+                               int day = 1,
+                               int hour = 0,
+                               int minute = 0,
+                               int second = 0,
+                               int millisecond = 0,
+                               bool isUtc = false]);
   external DateImplementation.now();
   external static int _brokenDownDateToMillisecondsSinceEpoch(
       int years, int month, int day, int hour, int minute, int second,
       int millisecond, bool isUtc);
   external String get timeZoneName;
   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;
 }