The new code is only exercised in tests so far. The H264 profile-level-id
parsing is not complete, but it should be enough for our purposes for
now.
BUG=webrtc:6400,webrtc:6337
Review-Url: https://codereview.webrtc.org/2459633002
Cr-Commit-Position: refs/heads/master@{#14850}