As Google says here you don’t have to specify something if you host your Chrome app in Google Servers. But why all the extensions I analysed had this code in their manifest.json. Should I also write this code in my chrome extensions manifest?
"update_url": "http://clients2.google.com/service/update2/crx",
As I said I will upload and share my app using chrome web store
You should remove “update_url” from manifest.json
Chrome automatically will update your extension from Web Store. So you should upload your extension to web Store.