Function syncUpdates

code/composition/public/app.js:13677–13685

(fn, a, b, c, d)

    }
  }
  function syncUpdates(fn, a, b, c, d) {
    var previousExpirationContext = expirationContext;
    expirationContext = Sync;
    try {
      return fn(a, b, c, d);
    } finally {
      expirationContext = previousExpirationContext;
    }
  }

  // TODO: Everything below this is written as if it has been lifted to the
  // renderers. I'll do this in a follow-up.