Reapply "Add support for timezone offset and timezone name."

tests/corelib/date_time7_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.
+
+// Test Date timeZoneName and timeZoneOffset getters.
+
+testUtc() {
+  var d = new Date.fromString("2012-03-04T03:25:38.123Z");
+  Expect.equals("UTC", d.timeZoneName);
+  Expect.equals(0, d.timeZoneOffset.inSeconds);
+}
+
+testLocal() {
+  checkOffset(String name, Duration offset) {
+    // Timezone abbreviations are not in bijection with their timezones.
+    // For example AST stands for "Arab Standard Time" (UTC+03), as well as
+    // "Arabian Standard Time" (UTC+04), or PST stands for Pacific Standard Time
+    // and Philippine Standard Time.
+    //
+    // Hardcode some common timezones.
+    if (name == "CET") {
+      Expect.equals(1, offset.inHours);
+    } else if (name == "CEST") {
+      Expect.equals(2, offset.inHours);
+    } else if (name == "GMT") {
+      Expect.equals(0, offset.inSeconds);
+    } else if (name == "EST") {
+      Expect.equals(-5, offset.inHours);
+    } else if (name == "EDT") {
+      Expect.equals(-4, offset.inHours);
+    } else if (name == "PDT") {
+      Expect.equals(-7, offset.inHours);
+    }
+  }
+
+  var d = new Date.fromString("2012-01-02T13:45:23");
+  String name = d.timeZoneName;
+  checkOffset(name, d.timeZoneOffset);
+
+  d = new Date.fromString("2012-07-02T13:45:23");
+  name = d.timeZoneName;
+  checkOffset(name, d.timeZoneOffset);
+}
+
+main() {
+  testUtc();
+  testLocal();
+}