Revert 12494.

lib/core/date.dart

Index: lib/core/date.dart
===================================================================
--- lib/core/date.dart	(revision 12500)
+++ lib/core/date.dart	(working copy)
@@ -13,7 +13,7 @@
  *
  * Also see [Stopwatch] for means to measure time-spans.
  */
-abstract class Date implements Comparable, Hashable {
+interface Date extends Comparable, Hashable default DateImplementation {
   // Weekday constants that are returned by [weekday] method:
   static const int MON = 1;
   static const int TUE = 2;
@@ -45,30 +45,27 @@
    * [month] and [day] are one-based. For example
    * [:new Date(1938, 1, 10)] represents the 10th of January 1938.
    */
-  factory Date(int year,
-               [int month = 1,
-                int day = 1,
-                int hour = 0,
-                int minute = 0,
-                int second = 0,
-                int millisecond = 0,
-                bool isUtc = false]) {
-    return new DateImplementation(year, month, day,
-                                  hour, minute, second,
-                                  millisecond, isUtc);
-  }
+  // TODO(floitsch): the spec allows default values in interfaces, but our
+  // tools don't yet. Eventually we want to have default values here.
+  Date(int year,
+       [int month,
+        int day,
+        int hour,
+        int minute,
+        int second,
+        int millisecond,
+        bool isUtc]);
 
   /**
    * Constructs a new [Date] instance with current date time value in the
    * local time zone.
    */
-  factory Date.now() => new DateImplementation.now();
+  Date.now();
 
   /**
    * Constructs a new [Date] instance based on [formattedString].
    */
-  factory Date.fromString(String formattedString)
-      => new DateImplementation.fromString(formattedString);
+  Date.fromString(String formattedString);
 
   /**
    * Constructs a new [Date] instance with the given [millisecondsSinceEpoch].
@@ -80,12 +77,7 @@
    */
   // TODO(floitsch): the spec allows default values in interfaces, but our
   // tools don't yet. Eventually we want to have default values here.
-  // TODO(lrn): Have two constructors instead of taking an optional bool.
-  factory Date.fromMillisecondsSinceEpoch(int millisecondsSinceEpoch,
-                                          [bool isUtc = false]) {
-    return new DateImplementation.fromMillisecondsSinceEpoch(
-        millisecondsSinceEpoch, isUtc);
-  }
+  Date.fromMillisecondsSinceEpoch(int millisecondsSinceEpoch, [bool isUtc]);
 
   /**
    * Returns true if [this] occurs at the same time as [other]. The