Tree-shaking unused superclass method named "error" fails

[nex3]

In the following code:

class Super {
  void error() {
    throw "super error";
  }
}

class Sub extends Super {
  void error() {
    throw "sub error";
  }
}

main() async {
  new Sub().error();
}

Super.error() is unreachable, but dart2js (as of 0c005a3) fails to tree-shake it:

$ dart2js test.dart
$ grep -n "super error" out.js
4936:        throw H.wrapException("super error");

This seems to be dependent on the name of the method. If I change it to error_():

class Super {
  void error_() {
    throw "super error";
  }
}

class Sub extends Super {
  void error_() {
    throw "sub error";
  }
}

main() async {
  new Sub().error_();
}

Super.error_() does seem to be tree-shaken:

$ dart2js test.dart
$ grep -n "super error" out.js
4936:        throw H.wrapException("super error");

This came up in practice when trying to reduce the code size of the http package and its dependencies.