code: public <T extends AbstractGoogleJsonClient.Builder> T fromOfflineAuth(T builder, OfflineAuth auth) {
      Preconditions.checkNotNull(builder);
      Preconditions.checkNotNull(auth);
      if(auth.hasApiKey()) {
        return fromApiKey(builder, auth.getApiKey());
      }
      return fromCredential(builder, auth.getCredential());
    }
docs: Prepare an AbstractGoogleJsonClient.Builder with the given OfflineAuth object.
  
  @param builder The builder to be prepared.
  @param auth The OfflineAuth
  @return The passed in builder, for easy chaining.