docs: function doGitHubEtagsMatch(projectName, depotName, branchName,
                              directoryToInstallIn) {
    return getEtagFromEtagFile(depotName, branchName, directoryToInstallIn)
      .then(function (etagFromFile) {
        if (!etagFromFile) {
          return false;
        }
  
        return httpRequestPromise('HEAD',
          getGitHubZipUrlObject(projectName, depotName, branchName))
          .then(function (res) {
            var etagFromHeadRequest = returnEtagFromResponse(res);
            return etagFromFile === etagFromHeadRequest;
          });
      });
  }