Adding support for Unified Plan offer/answer negotiation.

Adding support for Unified Plan offer/answer negotiation.

Though only to the mediasession.cc layer, before anyone gets too excited.

This layer takes in a simplified "options" struct and the current local description,
and generates a new offer/answer. Previously the options struct assumed there would
only be one media description per media type (audio/video), but it now supports
N number of audio/video descriptions.

The next step is to add the ability for PeerConnection/WebRtcSession to create
"options" to represent multiple RtpTransceivers, and apply the Unified Plan
descriptions correctly. Right now, only Plan B descriptions will be
generated in unit tests.

[Taylor Brandstetter, 2017-01-16 11:39:54]

Description was changed from

==========
Working on Unified Plan SDP. Got to line 1460 of mediasession.cc
...
Fixes related to codec negotiation.

New m= sections should try to use payload types from current m=
sections. But conflicts should be handled appropriately.

If two m= sections use the same payload type for two codecs, only the
first should be added.

If two m= sections use different payload types to represent the same
codec, only the first should be added.

If an m= section has an RTX codec, it should only be added if its
associated codec was also added. So if we have section 1 with PT 100,
section 2 with PT 101, RTX 102, we add PT 100, but can't add 101, and
can't add 102 because 101 already exists. So we end up with 104 at the
very end.
...
Got to line 1800
==========

to

==========
Adding support for Unified Plan offer/answer negotiation.

Though only to the mediasession.cc layer, before anyone gets too excited.

This layer takes in a simplified "options" struct and the current local
description,
and generates a new offer/answer. Previously the options struct assumed there
would
only be one media description per media type (audio/video), but it now supports
N number of audio/video descriptions.

The next step is to add the ability for PeerConnection/WebRtcSession to create
"options" to represent multiple RtpTransceivers, and apply the Unified Plan
descriptions correctly. Right now, unified plan descriptions will still only be
generated in unit tests.
==========

[Taylor Brandstetter, 2017-02-21 18:03:03]

Description was changed from

==========
Adding support for Unified Plan offer/answer negotiation.

Though only to the mediasession.cc layer, before anyone gets too excited.

This layer takes in a simplified "options" struct and the current local
description,
and generates a new offer/answer. Previously the options struct assumed there
would
only be one media description per media type (audio/video), but it now supports
N number of audio/video descriptions.

The next step is to add the ability for PeerConnection/WebRtcSession to create
"options" to represent multiple RtpTransceivers, and apply the Unified Plan
descriptions correctly. Right now, unified plan descriptions will still only be
generated in unit tests.
==========

to

==========
Adding support for Unified Plan offer/answer negotiation.

Though only to the mediasession.cc layer, before anyone gets too excited.

This layer takes in a simplified "options" struct and the current local
description,
and generates a new offer/answer. Previously the options struct assumed there
would
only be one media description per media type (audio/video), but it now supports
N number of audio/video descriptions.

The next step is to add the ability for PeerConnection/WebRtcSession to create
"options" to represent multiple RtpTransceivers, and apply the Unified Plan
descriptions correctly. Right now, only Plan B descriptions will be
generated in unit tests.
==========