function concatWithDeps(locale, outBaseName, outputWrapper, dependencies = []) {
  const localeForFileName = getLocaleForFileName(locale);
  // Get a list of the FirebaseUI JS and its dependencies.
  const srcs = dependencies.concat([getTmpJsPath(locale)]);
  const outputPath = `${DEST_DIR}/${outBaseName}__${localeForFileName}.js`;
  return compile(srcs, outputPath, {
    compilation_level: 'WHITESPACE_ONLY',
    output_wrapper: outputWrapper
  });
}
Concatenates the core FirebaseUI JS with its external dependencies, and
cleans up comments and whitespace in the dependencies.
@param {string} locale The desired FirebaseUI locale.
@param {string} outBaseName The prefix of the output file name.
@param {string} outputWrapper A wrapper with which to wrap the output JS.
@param {?Array<string>=} dependencies The dependencies to concatenate.
@return {*} A stream that ends when compilation finishes.