Add Future.timeout.

tests/lib/async/future_test.dart

Index: tests/lib/async/future_test.dart
diff --git a/tests/lib/async/future_test.dart b/tests/lib/async/future_test.dart
index ed342bc8439124f7c565c9f59eb5786a0b0c2976..20ae1c5190c5fa7ff963e5dc0a76e7a5cb443d64 100644
--- a/tests/lib/async/future_test.dart
+++ b/tests/lib/async/future_test.dart
@@ -808,6 +808,8 @@ class CustomFuture<T> implements Future<T> {
   Future catchError(Function onError, {bool test(e)}) =>
       _realFuture.catchError(onError, test: test);
   Future whenComplete(action()) => _realFuture.whenComplete(action);
+  Future timeout(Duration timeLimit, [void onTimeout()]) =>
+      _realFuture.timeout(timeLimit, onTimeout);
   Stream asStream() => _realFuture.asStream();
   String toString() => "CustomFuture@${_realFuture.hashCode}";
   int get hashCode => _realFuture.hashCode;