On "Disable Local Echo" For Desktop Audio Share

Can someone take a look at
https://github.com/w3c/mediacapture-screen-share/pull/44 ?

We tried to add a constraint entry for the GetUserMedia call, which is used
to control whether we mute the audio on the sender side during sharing.

The motivation we are trying to do it is that we have use cases for both.
1. For peer to peer connection, for example hangouts session or any other
video chat, when sharing audio, the user would in general expect that both
the sender and receiver can hear the sound.

2. For Cast, or any other app that is designed to project a laptop to the
big screen in the conference room, we would hope that only the receiver
(the speaker associated with the big screen) would play out the audio.

Thanks.