var foo = {
  'bar': 123
};
window.bar = function() {
  console.log(foo['bar']);
}

Turns into:

var foo = {
  bar: 123
};
window.bar = function() {
  console.log(foo['bar']);
}

Note that the object literal lost its explicit string encoding. This breaks Google Closure Compiler's advanced mode heuristic/convention around property name mangling. Uglify has this mode too.

Maybe an explicit mode would be good for this? Or should it be default?