 = functionName;
      const guid = tr.b.GUID.allocateSimple();
      this.measureName_ = `${groupName} ${functionName}`;
      if (opt_timestamp) {
        this.startMark_ = {startTime: opt_timestamp};
      } else {
        this.startMarkName_ = `${this.measureName} ${guid} start`;
      }
      this.endMark_ = undefined;
      this.endMarkName_ = `${this.measureName} ${guid} end`;

      window.performance.mark(this.startMarkName_);
    }

    get groupName() {
      return this.groupName_;
    }

    ge