get itemURL()
    {
        // I don't think this will work at all.
        return "cache://" + this._cache.cacheId;
    }
@constructor
@extends {WebInspector.BaseStorageTreeElement}
@param {!WebInspector.ResourcesPanel} storagePanel
@param {!WebInspector.ServiceWorkerCacheModel} model
@param {!WebInspector.ServiceWorkerCacheModel.Cache} cache