Only use replaced with FakePeriodicVideoTrackSource. Bug: webrtc:6353 Change-Id: Iee38b98a5242a292a848738bde05de18d96de7f4 Reviewed-on: https://webrtc-review.googlesource.com/79441 Reviewed-by: Steve Anton <steveanton@webrtc.org> Commit-Queue: Niels Moller <nisse@webrtc.org> Cr-Commit-Position: refs/heads/master@{#23441}