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

tests/language/vm/load_to_load_unaligned_forwarding_vm_test.dart

 // Copyright (c) 2012, 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.
 // Test correctness of side effects tracking used by load to load forwarding.
 // Should be merged into load_to_load_forwarding once Issue 22151 is fixed.
 
-// VMOptions=--optimization-counter-threshold=10
+// VMOptions=--optimization-counter-threshold=10 --no-background-compilation
 
 import "package:expect/expect.dart";
 import "dart:typed_data";
 
 testViewAliasing5() {
   final f32 = new Float32List(2);
   final raw = f32.buffer.asByteData();
   f32[0] = 1.5;  // Aliased by unaligned write of the same size.
   raw.setInt32(1, 0x00400000, Endianness.LITTLE_ENDIAN);
   return f32[0];
 }
 
 main() {
   for (var i = 0; i < 20; i++) {
     Expect.equals(2.0, testViewAliasing5());
   }
 }