initializeRunner = () => {
  if (goog.ASSUME_NATIVE_PROMISE ||
      (goog.global.Promise && goog.global.Promise.resolve)) {
    // Use goog.global.Promise instead of just Promise because the relevant
    // externs may be missing, and don't alias it because this could confuse the
    // compiler into thinking the polyfill is required when it should be treated
    // as optional.
    const promise = goog.global.Promise.resolve(undefined);
    schedule = () => {
      promise.then(run.processWorkQueue);
    };
  } else {
    schedule = () => {
      nextTick(run.processWorkQueue);
    };
  }
}
Initializes the function to use to process the work queue.