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

tests/language/sync_generator1_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.
 
 // Simple test program for sync* generator functions.
 
-// VMOptions=--optimization_counter_threshold=10
+// VMOptions=--optimization_counter_threshold=10 --no-background_compilation
 
 import "package:expect/expect.dart";
 
 sum10() sync* {
   var s = 0;
   for (var k = 1; k <= 10; k++) {
     s += k;
     yield s;
   }
 }
@@ skipping 58 matching lines @@
 
     print(sync);
     Expect.equals("sync", sync.single);
 
     print(einsZwei());
     Expect.equals("(1, 2, 3, 5, [6])", einsZwei().toString());
 
     Expect.throws(() => dreiVier().toString()); /// 01: continued
   }
 }