[1] App manifest - App Center | MDN ( 版) <https://developer.mozilla.org/en-US/Apps/Build/Manifest>
[2] Runtime and Security Model for Web Applications ( 版) <http://www.w3.org/TR/2015/NOTE-runtime-20150806/#serving-manifests>
When served as a static file, it is recommended that the manifest is stored with the extension .webapp. The manifest must be served with a Content-Type header of application/x-web-app-manifest+json. It is recommended that application manifests are served over SSL.