Timer callbacks don't take arguments anymore.

utils/pub/utils.dart

Index: utils/pub/utils.dart
diff --git a/utils/pub/utils.dart b/utils/pub/utils.dart
index e03343f56d94682f5d719cf1281de956185c04d4..6fe071f65b2950c90ef5b88179d3f34686e0416c 100644
--- a/utils/pub/utils.dart
+++ b/utils/pub/utils.dart
@@ -158,8 +158,7 @@ Future defer(callback()) {
 /// Returns a [Future] that completes in [milliseconds].
 Future sleep(int milliseconds) {
   var completer = new Completer();
-  new Timer(new Duration(milliseconds: milliseconds),
-      (_) => completer.complete());
+  new Timer(new Duration(milliseconds: milliseconds), completer.complete);
   return completer.future;
 }