async getArtifact(context) {
    const events = this.passivelyCollectBFCacheEvents(context);
    if (context.gatherMode === 'navigation' && !context.settings.usePassiveGathering) {
      const activelyCollectedEvent = await this.activelyCollectBFCacheEvent(context);
      if (activelyCollectedEvent) events.push(activelyCollectedEvent);
    }

    return events.map(BFCacheFailures.processBFCacheEvent);
  }
@param {LH.Gatherer.Context<'DevtoolsLog'>} context
@return {Promise<LH.Artifacts['BFCacheFailures']>}