_addEntry (requestData, cacheWhitelist) {
		var urlPath = requestData.urlPath,
			entries = this.dataCache[urlPath] || (this.dataCache[urlPath] = []),
			newEntry = new CacheEntry(this, requestData, cacheWhitelist);
		entries.push(newEntry);
		return newEntry
	}
Add a new CacheEntry for the request described by `requestData`

@param requestData the request data descriptor, as defined by
       Request._getCacheAffectingData.
@param cacheWhiteList the whitelist of fields that will be provided
       on the request.