Revert "Removes dartc reliance on its own libraries, now can be targeted at any implementation's li…

compiler/lib/implementation/time_zone_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.
+
+// JavaScript implementation of TimeZoneImplementation.
+class TimeZoneImplementation implements TimeZone {
+  const TimeZoneImplementation.utc() : this.isUtc = true;
+  const TimeZoneImplementation.local() : this.isUtc = false;
+
+  bool operator ==(other) {
+    if (!(other is TimeZoneImplementation)) return false;
+    return isUtc == other.isUtc;
+  }
+
+  String toString() {
+    if (isUtc) return "TimeZone (UTC)";
+    return "TimeZone (Local)";
+  }
+
+  final bool isUtc;
+}