Add VMOptions to optimize tests that need to be (Part I).

tests/language/compound_assignment_operator_test.dart

 // 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.
 // Tests that lhs of a compound assignement is executed only once.
+// VMOptions=--optimization-counter-threshold=10
 
 import "package:expect/expect.dart";
 
-
 class Indexed {
   Indexed() : _f = new List(10), count = 0 {
     _f[0] = 100;
     _f[1] = 200;
   }
   operator [](i) {
     count++;
     return _f;
   }
   var count;
@@ skipping 51 matching lines @@
 
     sequence(obj().field += 1, middle(), obj().field += 1);
     Expect.listEquals([0, 1, 2, 0, 1, 3], result);
 
     result = [];
     sequence(A.static_field++, middle(), A.static_field++);
     Expect.listEquals([0, 1, 2, 0, 1, 3], result);
   }
 
   static void testMain() {
-    for (int i = 0; i < 1000; i++) {
+    for (int i = 0; i < 20; i++) {
       testIndexed();
       testIndexedMore();
       testIndexedMoreMore();
     }
   }
 }
 
 main() {
   CompoundAssignmentOperatorTest.testMain();
 }