Revert of Make RtcEventLogImpl to use a TaskQueue instead of a helper-thread (patchset #4 id:200001 of https://codereview.webrtc.org/3005153002/ )

Reason for revert:
Landed without CQ, which was unintended.

Original issue's description:
> Reland of Make RtcEventLogImpl to use a TaskQueue instead of a helper-thread (patchset #1 id:1 of https://codereview.webrtc.org/3010143002/ )
>
> 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: https://chromium.googlesource.com/external/webrtc/+/f33cee7534f0469330b6b7aa57f84eec4b082598
> >
> > 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: https://chromium.googlesource.com/external/webrtc/+/3eac8002db8fdf5124026d5377a1f3ec1d16bb0d
>
> TBR=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}
> Committed: https://chromium.googlesource.com/external/webrtc/+/d67cefbbeab0a092d1fa250c811c25733dced043

TBR=terelius@webrtc.org,nisse@webrtc.org,kwiberg@webrtc.org,perkj@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/3007193002
Cr-Original-Commit-Position: refs/heads/master@{#19691}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 23814b7df733d11d7604bf5503aa36263a5fe35c
8 files changed