Reason for revert:
I will fix and reland.
Original issue's description:
> Revert of Make RtcEventLogImpl to use a TaskQueue instead of a helper-thread (patchset #18 id:340001 of https://codereview.webrtc.org/3007473002/ )
>
> Reason for revert:
> Breaks google3 project.
>
> Original issue's description:
> > Make RtcEventLogImpl to use a TaskQueue instead of a helper-thread
> >
> > Make RtcEventLogImpl to use a TaskQueue instead of a helper-thread. This will eventually allow us to run multiple log sessions on a single task-queue.
> >
> > BUG=webrtc:8142, webrtc:8143, webrtc:8145
> >
> > Review-Url: https://codereview.webrtc.org/3007473002
> > Cr-Commit-Position: refs/heads/master@{#19666}
> > Committed: f33cee7534
>
> TBR=terelius@webrtc.org,nisse@webrtc.org,eladalon@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:8142, webrtc:8143, webrtc:8145
>
> Review-Url: https://codereview.webrtc.org/3010143002
> Cr-Commit-Position: refs/heads/master@{#19672}
> Committed: 3eac8002dbTBR=terelius@webrtc.org,nisse@webrtc.org,charujain@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:8142, webrtc:8143, webrtc:8145
Review-Url: https://codereview.webrtc.org/3005153002
Cr-Commit-Position: refs/heads/master@{#19690}
d67cefbbea