async function loadFullVersions() {
  if (useUserAgentDataBrand(true)) {
    await fullVersionList.load();
  }
  preUachHasLoaded = true;
}
Requests all full browser versions to be cached.  When the returned promise
resolves, subsequent calls to `fullVersionOf(...).getIfLoaded()` will return
a value.

This method should be avoided in favor of directly awaiting
`fullVersionOf(...).load()` where it is used.

@return {!Promise<void>}