Revert of Do not block in SimpleThread::Start().

Revert of Do not block in SimpleThread::Start(). (patchset #6 id:100001 of https://codereview.chromium.org/2664953004/ )

Reason for revert:
Attempt to fix iOS Simulator issues with SkipOnShutdown/TaskSchedulerTaskTrackerTest.WillPostAndRunLongTaskBeforeShutdown/0

Original issue's description:
> Do not block in SimpleThread::Start().
> 
> There is no good reason to block in SimpleThread::Start().
> In addition to introducing unnecessary latency, blocking in
> Start() prevents a non-joinable DelegateSimpleThread from
> being deleted from Run() without external synchronization
> (it is wrong to delete SimpleThread while Start() is waiting
> on the |event_| member).
> 
> BUG=
> CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
> 
> Review-Url: https://codereview.chromium.org/2664953004
> Cr-Commit-Position: refs/heads/master@{#448622}
> Committed: https://chromium.googlesource.com/chromium/src/+/8ad2f4f9bb3d55974ea1707ff4186bbe321ea499

TBR=gab@chromium.org,jam@chromium.org,henrika@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review-Url: https://codereview.chromium.org/2685533003
Cr-Commit-Position: refs/heads/master@{#448658}
Committed: https://chromium.googlesource.com/chromium/src/+/40937c0272cf7ae2342b318cf394dbdaddaa5a76

[battre, 2017-02-07 17:39:44]

The CQ bit was checked by battre@chromium.org

[battre, 2017-02-07 17:39:45]

Created Revert of Do not block in SimpleThread::Start().

[commit-bot: I haz the power, 2017-02-07 17:40:11]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-02-07 17:40:59]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1486489184910920, "parent_rev":
"5660147465d3ca276ae8f93b512c1db5e3a73a33", "commit_rev":
"40937c0272cf7ae2342b318cf394dbdaddaa5a76"}

[commit-bot: I haz the power, 2017-02-07 17:41:43]

Description was changed from

==========
Revert of Do not block in SimpleThread::Start(). (patchset #6 id:100001 of
https://codereview.chromium.org/2664953004/ )

Reason for revert:
Attempt to fix iOS Simulator issues with
SkipOnShutdown/TaskSchedulerTaskTrackerTest.WillPostAndRunLongTaskBeforeShutdown/0

Original issue's description:
> Do not block in SimpleThread::Start().
> 
> There is no good reason to block in SimpleThread::Start().
> In addition to introducing unnecessary latency, blocking in
> Start() prevents a non-joinable DelegateSimpleThread from
> being deleted from Run() without external synchronization
> (it is wrong to delete SimpleThread while Start() is waiting
> on the |event_| member).
> 
> BUG=
>
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
> 
> Review-Url: https://codereview.chromium.org/2664953004
> Cr-Commit-Position: refs/heads/master@{#448622}
> Committed:
https://chromium.googlesource.com/chromium/src/+/8ad2f4f9bb3d55974ea1707ff418...

TBR=gab@chromium.org,jam@chromium.org,henrika@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=
==========

to

==========
Revert of Do not block in SimpleThread::Start(). (patchset #6 id:100001 of
https://codereview.chromium.org/2664953004/ )

Reason for revert:
Attempt to fix iOS Simulator issues with
SkipOnShutdown/TaskSchedulerTaskTrackerTest.WillPostAndRunLongTaskBeforeShutdown/0

Original issue's description:
> Do not block in SimpleThread::Start().
> 
> There is no good reason to block in SimpleThread::Start().
> In addition to introducing unnecessary latency, blocking in
> Start() prevents a non-joinable DelegateSimpleThread from
> being deleted from Run() without external synchronization
> (it is wrong to delete SimpleThread while Start() is waiting
> on the |event_| member).
> 
> BUG=
>
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
> 
> Review-Url: https://codereview.chromium.org/2664953004
> Cr-Commit-Position: refs/heads/master@{#448622}
> Committed:
https://chromium.googlesource.com/chromium/src/+/8ad2f4f9bb3d55974ea1707ff418...

TBR=gab@chromium.org,jam@chromium.org,henrika@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review-Url: https://codereview.chromium.org/2685533003
Cr-Commit-Position: refs/heads/master@{#448658}
Committed:
https://chromium.googlesource.com/chromium/src/+/40937c0272cf7ae2342b318cf394...
==========

[commit-bot: I haz the power, 2017-02-07 17:41:44]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/40937c0272cf7ae2342b318cf394...