async requestFileContent(path, callback) {
    const result = await this._fsIOService.readFile(this._rootURL + path, 'base64');
    if (this.contentType(path) === Common.resourceTypes.Image) {
      callback(result, true);
    } else {
      const content = await(await fetch(`data:application/octet-stream;base64,${result}`)).text();
      callback(content, false);
    }
  }
@override
@param {string} path
@param {function(?string,boolean)} callback