Add --no-background-compilation to tests that expect to run code in optimized form

tests/language/load_indexed_constant_test.dart

Index: tests/language/load_indexed_constant_test.dart
diff --git a/tests/language/load_indexed_constant_test.dart b/tests/language/load_indexed_constant_test.dart
index cf45b18250affe1454dde07e86f18ae026193878..57e480284a4e15b1453865c3edc2b2091f0598d2 100644
--- a/tests/language/load_indexed_constant_test.dart
+++ b/tests/language/load_indexed_constant_test.dart
@@ -2,7 +2,7 @@
 // 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.
 // Test constant propgation of load-indexed operations
-// VMOptions=--optimization-counter-threshold=10
+// VMOptions=--optimization-counter-threshold=10 --no-background-compilation
 
 import "package:expect/expect.dart";