sporadic SLD errors

[fippo]

on talky we were seeing very rare errors where setLocalDescription failed without any apparent effect. Here is what happened:

• remote sent session-initiate without any streams.
• setRemoteDescription is called. createAnswer (1) is called. Processing of remote actions resumes. PeerConnection is in have-remote-offer state.
• remote sent source-add. SRD is called. createAnswer (2) is called. PeerConnection is transitioning have-remote-offer -> have-remote-offer
• createAnswer (1) returns. setLocalDescription is called. PeerConnection goes into stable state. Things work.
• createAnswer (2) returns. setLocalDescription is called even though state is stable. Boom. But no bad things happened.

Proposed solution (other than continuing to work on the green spinning vortex of processing doom) is to ignore SLD when the state is stable.

[fippo]

hrm. Oddly, at least here the signalingstate is still have-remote-offer. But down in adapter it is stable and I don't see how that could change unless the signaling state is somehow magically updated in the background (which would seem like a stupid idea).

Further investigation needed.

[fippo]

so... the signaling state changes between createAnswer here (still have-remote-offer) and setLocalDescription here inside the callback from that. That means this workaround needs to be done in https://github.com/otalk/rtcpeerconnection
Alternatively we might skip createAnswer and immediately do SLD with the current description which is what Hangouts does.