Disable GVN for interceptors and fields.

tests/language/gvn_interceptor_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.
 
-class Bound {
-  run() {
-    return 42;
+foo(a, index) {
+  if (a.length < index) {
+   for (int i = a.length; i <= index; i++) a.add(i);
   }
+  // dart2js was reusing the a.length from above.
+  return a[a.length - 1];
 }
 
 void main() {
-  var runner = new Bound().run;
-  Expect.equals(42, runner());
+  Expect.equals(3, foo([0], 3));
 }