Make the repeating argument to timers optional.

runtime/bin/timer.dart

Index: runtime/bin/timer.dart
diff --git a/runtime/bin/timer.dart b/runtime/bin/timer.dart
index 34ea2c038c7f5973b5cdc06aea92278543482663..c6389b462637a6ae0c176f22d2bb8640cf8263fa 100644
--- a/runtime/bin/timer.dart
+++ b/runtime/bin/timer.dart
@@ -4,14 +4,19 @@
 
 interface Timer factory _Timer{
 
-  /*
+  /**
    * Creates a new timer. The [callback] callback is invoked after
-   * [milliSeconds] milliseconds. If [repeating] is set, the timer
-   * is repeated every [milliSeconds] milliseconds until cancelled.
+   * [milliSeconds] milliseconds.
    */
-  Timer(void callback(Timer timer), int milliSeconds, bool repeating);
+  Timer(void callback(Timer timer), int milliSeconds);
+ 
+  /**
+   * Creates a new repeating timer. The [callback] is invoked every
+   * [milliSeconds] millisecond until cancelled.
+   */
+  Timer.repeating(void callback(Timer timer), int milliSeconds);
 
-  /*
+  /**
    * Cancels the timer.
    */
   void cancel();