Added dependencies used by MockRtpTransportControllerSend to its header
file. The mocked interface can't be used properly without those.
This prepares for later CLs utilizing the mock.
Bug: None
Change-Id: I5f8ca04032ad09810240f7c034cc628d700dbedb
Reviewed-on: https://webrtc-review.googlesource.com/56181
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22154}