JSNull ClassMirror has itself in superinterfaces

[mraleph]

import 'dart:mirrors';

main() {
  final t = reflect(null).type;
  print(t.superinterfaces.contains(t));
}

would print true on dart2js.

This causes infinite recursion in anything that tries to traverse superinterfaces recursively (e.g. polymer_expression package).

[floitschG]

https://codereview.chromium.org/161333002

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Added Started label.

[floitschG]

Fixed in r32650

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Added Fixed label.