static processBFCacheEventList(errorList) {
    /** @type {LH.Artifacts.BFCacheNotRestoredReasonsTree} */
    const notRestoredReasonsTree = {
      Circumstantial: {},
      PageSupportNeeded: {},
      SupportPending: {},
    };

    for (const err of errorList) {
      const bfCacheErrorsMap = notRestoredReasonsTree[err.type];
      bfCacheErrorsMap[err.reason] = [];
    }

    return {notRestoredReasonsTree};
  }
@param {LH.Crdp.Page.BackForwardCacheNotRestoredExplanation[]} errorList
@return {LH.Artifacts.BFCacheFailure}