[manifest] List expected permissions in the manifest. (#395)

I was asked about permissions in the manifest today (see attached image).  Chrome currently exposes the list of user accepted permissions in the URL infobar and in the (i) icon on mobile, this is so that users can revoke or change the permission that they have granted.  If the user hasn't granted anything (maybe because they haven't yet been asked) the list is empty.

The request I received was to list permissions in the manifest and use that to enumerate a list in the browser chrome (in Chrome's case it might be to pre-populate this information menu so that it) to inform the user of what the site or app might ask for.

I might expect the permissions to be listed in the manifest as follows:
```
"permissions": [
  "notifications"
]
```
and take the same names as those used in the [permissions API registry](https://w3c.github.io/permissions/#permission-registry).  Specifying them in the manifest would not "pre-grant" access to these API's as they would be indicators of what the app needs at run-time.

<img width="726" alt="screen shot 2015-08-13 at 9 03 22 pm" src="https://cloud.githubusercontent.com/assets/45510/9260324/f3ab0638-41fe-11e5-824d-480c9331c507.png">

cc @mounirlamouri @marcoscaceres 



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Reply to this email directly or view it on GitHub:
https://github.com/w3c/manifest/issues/395