StorageEvent 构造函数
实现
factory StorageEvent(String type,
{bool canBubble = false,
bool cancelable = false,
String? key,
String? oldValue,
String? newValue,
String? url,
Storage? storageArea}) {
StorageEvent e = document._createEvent("StorageEvent") as StorageEvent;
e._initStorageEvent(
type, canBubble, cancelable, key, oldValue, newValue, url, storageArea);
return e;
}