code: function concatWithDeps(locale, outBaseName, outputWrapper) {
    const localeForFileName = getLocaleForFileName(locale);
    // Get a list of the FirebaseUI JS and its dependencies.
    const srcs = JS_DEPS.concat([getTmpJsPath(locale)]);
    const outputPath = `${DEST_DIR}/${outBaseName}__${localeForFileName}.js`;
    return compile(srcs, outputPath, {
      compilation_level: 'WHITESPACE_ONLY',
      output_wrapper: outputWrapper
    });
  }
docs: 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.
  @return {*} A stream that ends when compilation finishes.