Fix --compile_all flag (--compile-all is wrong)

runtime/observatory/tests/service/test_helper.dart

Index: runtime/observatory/tests/service/test_helper.dart
diff --git a/runtime/observatory/tests/service/test_helper.dart b/runtime/observatory/tests/service/test_helper.dart
index b9f3c7be42994627c1bdb48d052d30e969962372..f47f1cd45e9bfbf3778be5e9a793482a222146cf 100644
--- a/runtime/observatory/tests/service/test_helper.dart
+++ b/runtime/observatory/tests/service/test_helper.dart
@@ -1,7 +1,7 @@
 // Copyright (c) 2013, 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.
-// VMOptions=--compile-all --error_on_bad_type --error_on_bad_override --checked
+// VMOptions=--compile_all --error_on_bad_type --error_on_bad_override --checked
 
 library test_helper;