function forEachSingleChild(bookKeeping, child, name) {
  var func = bookKeeping.func,
      context = bookKeeping.context;

  func.call(context, child, bookKeeping.count++);
}
Verifies the object is a ReactElement.
See https://facebook.github.io/react/docs/top-level-api.html#react.isvalidelement
@param {?object} object
@return {boolean} True if `object` is a valid component.
@final