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

tests/language/number_identity2_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.
 // Dart test program for testing params.
 //
 // Contains test that is failing on dart2js. Merge this test with
 // 'number_identity_test.dart' once fixed.
-// VMOptions=--optimization-counter-threshold=10
+// VMOptions=--optimization-counter-threshold=10 --no-background-compilation
 
 import "package:expect/expect.dart";
 import 'dart:typed_data';
 
 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 10 matching lines @@
   a = 0.0/0.0;
   b = 1.0/0.0;
   Expect.isFalse(identical(a, b));
 }
 
 main() {
   for (int i = 0; i < 20; i++) {
     testNumberIdentity();
   }
 }