Reland of Use sched_yield on all POSIX platforms in PlatformThread. (patchset #1 id:1 of https://codereview.webrtc.org/2712133003/ )
Reland of Use sched_yield on all POSIX platforms in PlatformThread. (patchset #1 id:1 of https://codereview.webrtc.org/2712133003/ )

Reason for revert:
Relanding - using sched_yield() in PlatformThread on all posix platforms.

Original issue's description:
> Revert of Use sched_yield on all POSIX platforms in PlatformThread. (patchset #1 id:1 of https://codereview.webrtc.org/2716683002/ )
>
> Reason for revert:
> Reverting this change since it didn't affect the perf regressions we were seeing and actually seems to have caused more regressions as per comment in the bug.
>
> Original issue's description:
> > Use sched_yield on all POSIX platforms in PlatformThread.
> > (not only MacOS)
> >
> > This is a test to see if perf regressions we're seeing may be related to the use of nanosleep().
> >
> > BUG=695438
> > TBR=solenberg@webrtc.org
> >
> > Review-Url: https://codereview.webrtc.org/2716683002 .
> > Cr-Commit-Position: refs/heads/master@{#16807}
> > Committed: https://chromium.googlesource.com/external/webrtc/+/384498abb5a0dc3e871e437e56b4a556c3ec1023
>
> TBR=solenberg@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=695438
>
> Review-Url: https://codereview.webrtc.org/2712133003
> Cr-Commit-Position: refs/heads/master@{#16833}
> Committed: https://chromium.googlesource.com/external/webrtc/+/3ba1a8cd1b875dc7bfcb7075fe4f78d0dfe0ff98

TBR=solenberg@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=695438

Review-Url: https://codereview.webrtc.org/2725573002
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#16899}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 4974df41838367e4d50c42bef3be121c7ac6e331

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