Added log messages for some important call setup events:
- First audio RTP packet sent / received
- First RTP packet of the first video frame sent / received
- Last RTP packet of the first video frame sent / received
These timestamps should make it easier to measure how fast the call
becomes established from the user's perspective.
Committed:
https://crrev.com/98bb6640d22e9fe03696054b5e054f174db7739f
Cr-Commit-Position: refs/heads/master@{#12287}