Payload type -> RtpCodecParameters maps added for sender and receiver
side. It contains information that will be needed for RTCCodecStats[1]
dictionaries.
Video[Sender/Receiver]Info is updated with current codec payload type
for every stream which can be used to look up the codec in
VideoMediaInfo.
A similar change should be made for VoiceMediaInfo and
Voice[Sender/Receiver]Info.
[1] https://w3c.github.io/webrtc-stats/#codec-dict*
BUG=chromium:659117
Review-Url: https://codereview.webrtc.org/2484193002
Cr-Commit-Position: refs/heads/master@{#15060}
a65704b5c9