Remove assumption that all video codecs are known.
Remove assumption that all video codecs are known.

Bug: webrtc:9516
Change-Id: I810e9bfe556e6d2ccfeb7a35f7c6785c9909a0e2
Reviewed-on: https://webrtc-review.googlesource.com/94512
Reviewed-by: Sebastian Jansson <c24d1bc144eb7c11e553f59153fa17dba85ca83e@webrtc.org>
Reviewed-by: Rasmus Brandt <9545de3a34b925a736ae2b5ee593f3033f743a28@webrtc.org>
Commit-Queue: Kári Helgason <79949f6d84ac41ff1f64c59fd5a554be5ff12a02@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#24420}
TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc