Disable GVN for interceptors and fields.

tests/language/gvn_field_access_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;
+class A {
+  var y = 0;
+  foo(x) {
+    var t = this.y;
+    if (t < x) {
+      for (int i = this.y; i < x; i++) y++;
+    }
+    // dart2js was reusing the 't' from above.
+    return this.y;
   }
 }
 
 void main() {
-  var runner = new Bound().run;
-  Expect.equals(42, runner());
+  Expect.equals(3, new A().foo(3));
 }