To avoid unnecessary repeating tasks, TaskQueuePacedSender is started
only upon RtpTransportControllerSend::EnsureStarted().
More specifically, the repeating task happens in
TaskQueuePacedSender::MaybeProcessPackets() every 500ms, using a self
task_queue_.PostDelayedTask().
Bug: chromium:1152887
Change-Id: I72c96d2c4b491d5edb45a30b210b3797165cbf48
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/208560
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33421}