The overlap in functionality is quite limited and separating the
functionality makes it a bit easier to follow each. This prepares
for adding a SimulatedThread class in a follow up CL.
Bug: webrtc:11255
Change-Id: I83c754bd570113dfb582098bb4d39e27bb4f4d87
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/165688
Reviewed-by: Jonas Olsson <jonasolsson@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30229}
