restoreTilesThatShareOriginalCache(tile, originalCache, freeIfUnused) {
            for (let t of originalCache._tiles) {
                if (t.cacheKey !== t.originalCacheKey) {
                    this.unloadCacheForTile(t, t.cacheKey, freeIfUnused, true);
                    delete t._caches[t.cacheKey];
                    t.cacheKey = t.originalCacheKey;
                }
            }
        }
This method ensures other tiles are restored if one of the tiles
was requested restore().
@param tile
@param originalCache
@param freeIfUnused if true, zombie is not created
@private