handleG2_(controlCode) {
    if (!this.currentWindow_) {
      return;
    }
    if (!shaka.cea.Cea708Service.G2Charset.has(controlCode)) {
      // If the character is unsupported, the spec says to put an underline.
      this.currentWindow_.setCharacter('_');
      return;
    }

    const char = shaka.cea.Cea708Service.G2Charset.get(controlCode);
    this.currentWindow_.setCharacter(char);
  }
Handles G2 group data.
@param {number} controlCode
@private