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

tests/standalone/unboxed_int_converter_test.dart

Index: tests/standalone/unboxed_int_converter_test.dart
diff --git a/tests/standalone/unboxed_int_converter_test.dart b/tests/standalone/unboxed_int_converter_test.dart
index 2b75a01be58ed503ef63e65caa0e08ace01d6068..297861d6b4b893ea157d6340088f3a08a14b8e86 100644
--- a/tests/standalone/unboxed_int_converter_test.dart
+++ b/tests/standalone/unboxed_int_converter_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 UnboxedIntConverter for int32.
-// VMOptions=--optimization-counter-threshold=10 --no-use-osr
+// VMOptions=--optimization-counter-threshold=10 --no-use-osr --no-background-compilation
 
 import "package:expect/expect.dart";
 import "dart:typed_data";