[webrtc-pc] new commits pushed by aboba

The following commits were just pushed by aboba to https://github.com/w3c/webrtc-pc:

* Annotate all interfaces with Exposed extended attribute

WebIDL is moving to making it a required extended attribute https://github.com/heycam/webidl/issues/365
  by Dominique Hazael-Massieux
https://github.com/w3c/webrtc-pc/commit/ec481e2e4ded42855e44b5e65fd5942094635fca

* Merge pull request #1572 from w3c/exposed

Annotate all interfaces with Exposed extended attribute
  by Bernard Aboba
https://github.com/w3c/webrtc-pc/commit/0db28f3bcfc9022b046b409be9b94c3e8ab00e83