Remove pseudo-shared Timer implementation.

tools/dom/src/Timer.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.
-
-part of html;
-
-class _Timer implements Timer {
-  final canceller;
-
-  _Timer(this.canceller);
-
-  void cancel() { canceller(); }
-}
-
-get _timerFactoryClosure => (int milliSeconds, void callback(Timer timer), bool repeating) {
-  var maker;
-  var canceller;
-  if (repeating) {
-    maker = window._setInterval;
-    canceller = window._clearInterval;
-  } else {
-    maker = window._setTimeout;
-    canceller = window._clearTimeout;
-  }
-  Timer timer;
-  final int id = maker(() { callback(timer); }, milliSeconds);
-  timer = new _Timer(() { canceller(id); });
-  return timer;
-};
-
-class _PureIsolateTimer implements Timer {
-  final ReceivePort _port = new ReceivePort();
-  SendPort _sendPort; // Effectively final.
-
-  static SendPort _SEND_PORT;
-
-  _PureIsolateTimer(int milliSeconds, callback, repeating) {
-    _sendPort = _port.toSendPort();
-    _port.receive((msg, replyTo) {
-      assert(msg == _TIMER_PING);
-      callback(this);
-      if (!repeating) _cancel();
-    });
-
-    _send([_NEW_TIMER, milliSeconds, repeating]);
-  }
-
-  void cancel() {
-    _cancel();
-    _send([_CANCEL_TIMER]);
-  }
-
-  void _cancel() {
-    _port.close();
-  }
-
-  _send(msg) {
-    _sendToHelperIsolate(msg, _sendPort);
-  }
-}
-
-get _pureIsolateTimerFactoryClosure =>
-    ((int milliSeconds, void callback(Timer time), bool repeating) =>
-        new _PureIsolateTimer(milliSeconds, callback, repeating));