The base implementation of `_.keysIn` which doesn't treat sparse arrays as dense.

@private
@param {Object} object The object to query.
@returns {Array} Returns the array of property names.
function baseKeysIn(object) {
  if (!isObject(object)) {
    return nativeKeysIn(object);
  }
  var isProto = isPrototype(object),
      result = [];

  for (var key in object) {
    if (!(key == 'constructor' && (isProto || !hasOwnProperty$b.call(object, key)))) {
      result.push(key);
    }
  }
  return result;
}