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

runtime/bin/timer_impl.dart

Index: runtime/bin/timer_impl.dart
diff --git a/runtime/bin/timer_impl.dart b/runtime/bin/timer_impl.dart
index ed7884251a0af25047871605c5739ece9287479d..b55923fc7f1e485825f43bf99bba2f0c2bd9e9a3 100644
--- a/runtime/bin/timer_impl.dart
+++ b/runtime/bin/timer_impl.dart
@@ -26,11 +26,11 @@ class _Timer implements Timer {
     return timer;
   }
 
-  factory _Timer(void callback(Timer timer), int milliSeconds) {
+  factory _Timer(int milliSeconds, void callback(Timer timer)) {
     return _createTimer(callback, milliSeconds, false);
   }
 
-  factory _Timer.repeating(void callback(Timer timer), int milliSeconds) {
+  factory _Timer.repeating(int milliSeconds, void callback(Timer timer)) {
     return _createTimer(callback, milliSeconds, true);
   }