Update Timer API to take the callback as the last parameter.

tests/standalone/src/io/TimerTest.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:io");
 
 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()).value;
       Expect.equals(true, (endTime - _startTime) >= _timeout);
       if (_iteration < _ITERATIONS) {
         _iteration++;
         _timeout = _timeout - _DECREASE;
         _startTime = (new Date.now()).value;
-        new Timer(timeoutHandler, _timeout);
+        new Timer(_timeout, timeoutHandler);
       }
     }
 
     _iteration = 0;
     _timeout = _STARTTIMEOUT;
     _startTime = (new Date.now()).value;
-     new Timer(timeoutHandler, _timeout);
+    new Timer(_timeout, timeoutHandler);
   }
 
   static void testMain() {
     testSimpleTimer();
   }
 
   static int _startTime;
   static int _timeout;
   static int _iteration;
 }
 
 main() {
   TimerTest.testMain();
 }