Restrict some JS names that we might use in our JS blocks. It doesn't break for now because our JS …

tests/compiler/dart2js_native/foreign_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.
 
 import 'dart:_foreign_helper' show JS;
 
 foreign1(var a, var b) {
   return JS("num", r"# + #", a, b);
 }
 
@@ skipping 12 matching lines @@
 foreign11(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11) {
   return JS("num", r"# + # + # + # + # + # + # + # + # + # + #",
       a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11);
 }
 
 void main() {
   Expect.equals(9, foreign1(4, 5));
   Expect.equals(998, foreign2());
   Expect.equals('1234567891011',
       foreign11('1', '2', '3', '4', '5', '6', '7', '8', '9', '10', '11'));
+  // Ensure there will be isNaN and NaN variable names.
+  var isNaN = called ? 42 : 44;
+  var NaN = called ? 52 : 54;
+  Expect.isFalse(JS('bool', 'isNaN(#)', isNaN));
+  Expect.isFalse(JS('bool', 'isNaN(#)', NaN));
+  Expect.isTrue(JS('bool', 'isNaN(#)', double.NAN));
 }