onBufferingStateChange_() {
    if (!this.enabled_) {
      return;
    }

    if (this.ad_ && this.ad_.isClientRendering() && this.ad_.isLinear()) {
      shaka.ui.Utils.setDisplay(this.spinnerContainer_, false);
      return;
    }

    shaka.ui.Utils.setDisplay(
        this.spinnerContainer_, this.player_.isBuffering());
  }
Called both as an event listener and directly by the controls to initialize
the buffering state.
@private