function mapKeys(object, iteratee) {
      var result = {};
      iteratee = getIteratee(iteratee, 3);

      baseForOwn(object, function(value, key, object) {
        result[iteratee(value, key, object)] = value;
      });
      return result;
    }
The opposite of `_.mapValues`; this method creates an object with the
same values as `object` and keys generated by running each own enumerable
string keyed property of `object` thru `iteratee`. The iteratee is invoked
with three arguments: (value, key, object).

@static
@memberOf _
@since 3.8.0
@category Object
@param {Object} object The object to iterate over.
@param {Array|Function|Object|string} [iteratee=_.identity]
 The function invoked per iteration.
@returns {Object} Returns the new mapped object.
@see _.mapValues
@example

_.mapKeys({ 'a': 1, 'b': 2 }, function(value, key) {
  return key + value;
});
// => { 'a1': 1, 'b2': 2 }