This cl change so that all encoder configuration changes are reported to VideoSendStream through the ViEEncoder.
Also, the PayLoadRouter is changed to never stop sending on a an ssrc due to the encoder video frame size changes. Instead, the number of sending streams is only decided by the number of sending ssrc.
This cl is a preparation for moving encoder reconfiguration due to input video frame size changes from WebRtcVideoSendStream to ViEEncoder.
BUG=webrtc:5687, webrtc:6371
R=mflodman@webrtc.org
Review URL: https://codereview.webrtc.org/2338133003 .
Cr-Commit-Position: refs/heads/master@{#14371}