Add Timer implementation for dart2js. Also moves tests to appropriate location.

tests/standalone/io/timer_test.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.
-
-#import("dart:isolate");
-
-class TimerTest {
-
-  static final int _STARTTIMEOUT = 1050;
-  static final int _DECREASE = 200;
-  static final int _ITERATIONS = 5;
-
-  static void testSimpleTimer() {
-
-    void timeoutHandler(Timer timer) {
-      int endTime = (new Date.now()).millisecondsSinceEpoch;
-      Expect.equals(true, (endTime - _startTime) >= _timeout);
-      if (_iteration < _ITERATIONS) {
-        _iteration++;
-        _timeout = _timeout - _DECREASE;
-        _startTime = (new Date.now()).millisecondsSinceEpoch;
-        new Timer(_timeout, timeoutHandler);
-      }
-    }
-
-    _iteration = 0;
-    _timeout = _STARTTIMEOUT;
-    _startTime = (new Date.now()).millisecondsSinceEpoch;
-    new Timer(_timeout, timeoutHandler);
-  }
-
-  static void testMain() {
-    testSimpleTimer();
-  }
-
-  static int _startTime;
-  static int _timeout;
-  static int _iteration;
-}
-
-main() {
-  TimerTest.testMain();
-}