Add DateTime.replace.

tests/corelib/date_time_replace_test.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.
+
+import "package:expect/expect.dart";
+
+testReplace(DateTime original,
+            int year, int month, int day, int hour,
+            int minute, int second, int millisecond,
+            bool isUtc) {
+  var result = original.replace(year: year, month: month, day: day,
+                                hour: hour, minute: minute, second: second,
+                                millisecond: millisecond, isUtc: isUtc);
+  var expected = isUtc
+      ? new DateTime.utc(
+            year ?? original.year,
+            month ?? original.month,
+            day ?? original.day,
+            hour ?? original.hour,
+            minute ?? original.minute,
+            second ?? original.second,
+            millisecond ?? original.millisecond)
+      : new DateTime(
+            year ?? original.year,
+            month ?? original.month,
+            day ?? original.day,
+            hour ?? original.hour,
+            minute ?? original.minute,
+            second ?? original.second,
+            millisecond ?? original.millisecond);
+
+  Expect.equals(expected, result);
+}
+
+main() {
+  var epoch = DateTime.parse("1970-01-01");
+  var dst = DateTime.parse("2015-07-07T12:12:24Z");
+  var leap = DateTime.parse("2012-02-28T12:12:24");
+
+  for (var year in [null, -100, 1917, 2012]) {
+    for (var month in [null, -1, 1, 12, 14]) {
+      for (var day in [null, -1, 1, 28, 29, 30, 31, 32]) {
+        for (var hour in [null, -1, 0, 23, 25]) {
+          for (var minute in [null, -1, 1, 59, 61]) {
+            for (var second in [null, -1, 1, 59, 61]) {
+              for (var millisecond in [null, -1, 1, 999, 1001]) {
+                for (var isUtc in [false, true]) {
+                  for (var base in [epoch, dst, leap]) {
+                    testReplace(base, year, month, day,
+                                hour, minute, second, millisecond, isUtc);
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}