static async compute_(trace) {
    return trace.traceEvents
      .filter(evt => evt.name === SCREENSHOT_TRACE_NAME)
      .map(evt => {
        return {
          timestamp: evt.ts,
          datauri: `data:image/jpeg;base64,${evt.args.snapshot}`,
        };
      });
  }
@param {LH.Trace} trace
@return {Promise<Array<{timestamp: number, datauri: string}>>}