code: function calculateCommonRecentCommand(archiveA, archiveB) {
      var historyA = archiveA._getWestley().getHistory(),
          historyB = archiveB._getWestley().getHistory(),
          aLen = historyA.length,
          bLen = historyB.length,
          a,
          b;
      for (a = aLen - 1; a >= 0; a -= 1) {
          if (getCommandType(historyA[a]) === "pad") {
              var paddingA = getPaddingID(historyA[a]);
              for (b = bLen - 1; b >= 0; b -= 1) {
                  if (getCommandType(historyB[b]) === "pad" && getPaddingID(historyB[b]) === paddingA) {
                      return {
                          a: a,
                          b: b,
                          historyA: historyA,
                          historyB: historyB
                      };
                  }
              }
          }
      }
      return false;
  }
docs: Calculate the common command indexes between 2 archives.
  The common index is where a padding ID matches that of the other archive,
  at some point. If we assume one archive may have been flattened, we cannot
  assume that the entire past history of the archives will be the same, but
  we can assume that at that point, the archives produce the same structure.
  Because the archives may be different in the future, we use the newest
  matching pad ID to create a common link between the 2 histories.
  @param {Archive} archiveA The original archive
  @param {Archive} archiveB The secondary archive
  @returns {Boolean|{ a: Number, b: Number, historyA: Array, historyB: Array }} Returns
  false if no common point, or an object with the common information. `a` and `b`
  are the indexes where the common padding occurs, and historyA and historyB are
  the history arrays for the archives.
  @private
  @static
  @memberof ArchiveComparator