docs: @GuardedBy("mLock")
    private boolean maybeUpdateFileCacheSize() {
      long now = mClock.now();
      if ((!mCacheStats.isInitialized()) ||
          mCacheSizeLastUpdateTime == UNINITIALIZED ||
          (now - mCacheSizeLastUpdateTime) > FILECACHE_SIZE_UPDATE_PERIOD_MS) {
        return maybeUpdateFileCacheSizeAndIndex();
      }
      return false;
    }