So that we don't have to be capable of creating one ourselves, which requires a dependency on the audio codecs. BUG=webrtc:8396 Change-Id: I5600da5e17f613b0e61a9fb0fbdb373fe42f855c Reviewed-on: https://webrtc-review.googlesource.com/20220 Reviewed-by: Peter Thatcher <pthatcher@webrtc.org> Commit-Queue: Karl Wiberg <kwiberg@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20641}