controlRcl_() {
    this.type_ = shaka.cea.Cea608DataChannel.CaptionType.POPON;
    this.curBuf_ = this.nonDisplayedMemory_;
    // No scroll window now
    this.curBuf_.setScrollSize(0);
  }
Handles RCL - Resume Caption Loading
Initiates Pop-On style captioning. No need to force anything out upon
entering Pop-On mode because it does not affect the current display.
@private