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

tests/lib/math/double_pow_test.dart

Index: tests/lib/math/double_pow_test.dart
diff --git a/tests/lib/math/double_pow_test.dart b/tests/lib/math/double_pow_test.dart
index 4736b5c0934cb519f71e41fb2449e1625bf07f2a..83a8ecea99790e814503af74d9b5ebad74bf029e 100644
--- a/tests/lib/math/double_pow_test.dart
+++ b/tests/lib/math/double_pow_test.dart
@@ -1,7 +1,7 @@
 // Copyright (c) 2011, 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=--optimization-counter-threshold=5
+// VMOptions=--optimization-counter-threshold=5 --no-background-compilation
 
 library math_test;
 import "package:expect/expect.dart";