Rework Timer interface.

tests/language/closure_cycles_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.
 // Based on dartbug.com/7681
 // Verify that context chains do not lead to unintended memory being held.
 
 library closure_cycles_test;
 
 import "dart:async";
 
 class X {
   Function onX;
-  X() { new Timer(0, (_) => onX(new Y())); }
+  X() { Timer.run(() => onX(new Y())); }
 }
 
 class Y {
   Function onY;
   var heavyMemory;
   static var count = 0;
   Y() {
     // Consume large amounts of memory per iteration to fail/succeed quicker.
     heavyMemory = new List(10*1024*1024);
     // Terminate the test if we allocated enough memory without running out.
     if (count++ > 100) return;
-    new Timer(0, (_) => onY());
+    Timer.run(() => onY());
   }
 }
 
 void doIt() {
   var x = new X();
   x.onX = (y) {
     y.onY = () {
       y;  // Capturing y can lead to endless context chains!
       doIt();
     };
   };
 }
 
 void main() {
   doIt();
 }