A preparation for deleting EventFactory and EventWrapper, to instead
use rtc::Event directly.
Bug: webrtc:3380
Change-Id: I4c40daca9268e57b06d506d91e09365091c42ad6
Reviewed-on: https://webrtc-review.googlesource.com/c/109880
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25545}