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

tests/isolate/timer_cancel1_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.
 
+#library('timer_cancel1_test');
+
 #import("dart:isolate");
 
 // Test that a timeout handler can cancel another.
 class TimerCancel1Test {
   static void testOtherCancel() {
     var canceleeTimer;
     var cancelerTimer;
 
     void timeoutHandlerUnreachable(Timer timer) {
       Expect.fail("A canceled timeout handler should be unreachable.");
     }
 
     void cancelHandler(Timer timer) {
       canceleeTimer.cancel();
     }
 
     cancelerTimer = new Timer(1, cancelHandler);
     canceleeTimer = new Timer(1000, timeoutHandlerUnreachable);
   }
 
   static void testMain() {
     testOtherCancel();
   }
 }
 
 main() {
   TimerCancel1Test.testMain();
 }