deps/v8/src/js/i18n.js
function initializeBreakIterator(iterator, locales, options) {
  if (%IsInitializedIntlObject(iterator)) {
    throw MakeTypeError(kReinitializeIntl, "v8BreakIterator");
  }

  if (IS_UNDEFINED(options)) {
    options = {};
  }

  var getOption = getGetOption(options, 'breakiterator');

  var internalOptions = {};

  defineWEProperty(internalOptions, 'type', getOption(
    'type', 'string', ['character', 'word', 'sentence', 'line'], 'word'));

  var locale = resolveLocale('breakiterator', locales, options);
  var resolved = %object_define_properties({}, {
    requestedLocale: {value: locale.locale, writable: true},
    type: {value: internalOptions.type, writable: true},
    locale: {writable: true}
  });

  var internalIterator = %CreateBreakIterator(locale.locale,
                                              internalOptions,
                                              resolved);

  %MarkAsInitializedIntlObjectOfType(iterator, 'breakiterator',
                                     internalIterator);
  iterator[resolvedSymbol] = resolved;
  if (FLAG_intl_extra) {
    %object_define_property(iterator, 'resolved', resolvedAccessor);
  }

  return iterator;
}
function initializeBreakIterator(iterator, locales, options) {
  if (%IsInitializedIntlObject(iterator)) {
    throw MakeTypeError(kReinitializeIntl, "v8BreakIterator");
  }

  if (IS_UNDEFINED(options)) {
    options = {};
  }

  var getOption = getGetOption(options, 'breakiterator');

  var internalOptions = {};

  defineWEProperty(internalOptions, 'type', getOption(
    'type', 'string', ['character', 'word', 'sentence', 'line'], 'word'));

  var locale = resolveLocale('breakiterator', locales, options);
  var resolved = %object_define_properties({}, {
    requestedLocale: {value: locale.locale, writable: true},
    type: {value: internalOptions.type, writable: true},
    locale: {writable: true}
  });

  var internalIterator = %CreateBreakIterator(locale.locale,
                                              internalOptions,
                                              resolved);

  %MarkAsInitializedIntlObjectOfType(iterator, 'breakiterator',
                                     internalIterator);
  iterator[resolvedSymbol] = resolved;
  if (FLAG_intl_extra) {
    %object_define_property(iterator, 'resolved', resolvedAccessor);
  }

  return iterator;
}
Initializes the given object so it's a valid BreakIterator instance.
Useful for subclassing.