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

tests/language/nan_identical_test.dart

 // Copyright (c) 2015, 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 a new statement by itself.
-// VMOptions=--optimization-counter-threshold=4
+// VMOptions=--optimization-counter-threshold=4 --no-background-compilation
 
 import 'dart:typed_data';
 
 import "package:expect/expect.dart";
 
 double uint64toDouble(int i) {
   var buffer = new Uint8List(8).buffer;
   var bdata = new ByteData.view(buffer);
   bdata.setUint64(0, i);
   return bdata.getFloat64(0);
@@ skipping 26 matching lines @@
     Expect.isFalse(checkIdentical(-a, -b));
     Expect.isFalse(checkIdentical(-a, b));
     Expect.isFalse(checkIdentical(a, -b));
 
     Expect.isTrue(checkIdentical(-(-a), a));
     Expect.isTrue(checkIdentical(-(-b), b));
   }
 }
 
 checkIdentical(a, b) => identical(a, b);