Make the repeating argument to timers optional.

runtime/bin/timer_impl.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.
 
 class _Timer implements Timer {
 
   /*
    * Set jitter to wake up timer events that would happen in _TIMER_JITTER ms.
    */
   static final int _TIMER_JITTER = 0;
 
   /*
    * Disables the timer.
    */
   static final int _NO_TIMER = -1;
 
-  factory _Timer(void callback(Timer timer),
-                 int milliSeconds,
-                 bool repeating) {
+  static Timer _createTimer(void callback(Timer timer),
+                           int milliSeconds,
+                           bool repeating) {
     EventHandler._start();
     if (_timers === null) {
       _timers = new DoubleLinkedQueue<_Timer>();
     }
     Timer timer = new _Timer._internal();
     timer._callback = callback;
     timer._milliSeconds = milliSeconds;
     timer._wakeupTime = (new Date.now()).value + milliSeconds;
     timer._repeating = repeating;
     timer._addTimerToList();
     timer._notifyEventHandler();
     return timer;
   }
 
+  factory _Timer(void callback(Timer timer), int milliSeconds) {
+    return _createTimer(callback, milliSeconds, false);
+  }
+
+  factory _Timer.repeating(void callback(Timer timer), int milliSeconds) {
+    return _createTimer(callback, milliSeconds, true);
+  }
+
   _Timer._internal() {}
 
   void _clear() {
     _callback = null;
     _milliSeconds = 0;
     _wakeupTime = 0;
     _repeating = false;
   }
 
   /*
@@ skipping 133 matching lines @@
 
   static ReceivePort _receivePort;
   static bool _handling_callbacks = false;
 
   var _callback;
   int _milliSeconds;
   int _wakeupTime;
   bool _repeating;
 }