Revert of Disallow posting tasks to SequencedWorkerPools by default.

Revert of Disallow posting tasks to SequencedWorkerPools by default. (patchset #25 id:480001 of https://codereview.chromium.org/2445763002/ )

Reason for revert:
chrome --mash crashing.

Original issue's description:
> Disallow posting tasks to SequencedWorkerPools by default.
>
> We have observed crash reports in which SequencedWorkerPool workers
> were active while redirection to TaskScheduler was enabled. This can
> happen if a task is posted to a SequencedWorkerPool before redirection
> to TaskScheduler is enabled. With this CL, DumpWithoutCrashing() is
> called if a task is posted to a SequencedWorkerPool too early. This
> will help us find offending call sites.
>
> A commented DCHECK is also added to find offending call sites. It
> will be uncommented in a separate CL to avoid a revert of this CL
> in case it fails on the waterfall.
>
> BUG=622400
>
> Committed: https://crrev.com/4606ada249a240e115a08a7c66409e8fdd457ea1
> Committed: https://crrev.com/8fd22217395d50b6704109c7f1d4deff59f9a109
> Cr-Original-Commit-Position: refs/heads/master@{#432913}
> Cr-Commit-Position: refs/heads/master@{#433237}

TBR=gab@chromium.org,brettw@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=622400
Committed: https://crrev.com/47c895a15251dde93c04721480cc9f1172d52cca
Cr-Commit-Position: refs/heads/master@{#433267}

[Fady Samuel, 2016-11-18 19:34:13]

The CQ bit was checked by fsamuel@chromium.org

[Fady Samuel, 2016-11-18 19:34:14]

Created Revert of Disallow posting tasks to SequencedWorkerPools by default.

[commit-bot: I haz the power, 2016-11-18 19:35:55]

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

[gab, 2016-11-18 19:36:56]

> Reason for revert:
> chrome --mash crashing.

1) Why is this not on CQ?
2) Why does debug::DumpWithoutCrashing() crash chrome --mash ?

[commit-bot: I haz the power, 2016-11-18 19:37:31]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-11-18 19:40:17]

Description was changed from

==========
Revert of Disallow posting tasks to SequencedWorkerPools by default. (patchset
#25 id:480001 of https://codereview.chromium.org/2445763002/ )

Reason for revert:
chrome --mash crashing.

Original issue's description:
> Disallow posting tasks to SequencedWorkerPools by default.
> 
> We have observed crash reports in which SequencedWorkerPool workers
> were active while redirection to TaskScheduler was enabled. This can
> happen if a task is posted to a SequencedWorkerPool before redirection
> to TaskScheduler is enabled. With this CL, DumpWithoutCrashing() is
> called if a task is posted to a SequencedWorkerPool too early. This
> will help us find offending call sites.
> 
> A commented DCHECK is also added to find offending call sites. It
> will be uncommented in a separate CL to avoid a revert of this CL
> in case it fails on the waterfall.
> 
> BUG=622400
> 
> Committed: https://crrev.com/4606ada249a240e115a08a7c66409e8fdd457ea1
> Committed: https://crrev.com/8fd22217395d50b6704109c7f1d4deff59f9a109
> Cr-Original-Commit-Position: refs/heads/master@{#432913}
> Cr-Commit-Position: refs/heads/master@{#433237}

TBR=gab@chromium.org,brettw@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=622400
==========

to

==========
Revert of Disallow posting tasks to SequencedWorkerPools by default. (patchset
#25 id:480001 of https://codereview.chromium.org/2445763002/ )

Reason for revert:
chrome --mash crashing.

Original issue's description:
> Disallow posting tasks to SequencedWorkerPools by default.
>
> We have observed crash reports in which SequencedWorkerPool workers
> were active while redirection to TaskScheduler was enabled. This can
> happen if a task is posted to a SequencedWorkerPool before redirection
> to TaskScheduler is enabled. With this CL, DumpWithoutCrashing() is
> called if a task is posted to a SequencedWorkerPool too early. This
> will help us find offending call sites.
>
> A commented DCHECK is also added to find offending call sites. It
> will be uncommented in a separate CL to avoid a revert of this CL
> in case it fails on the waterfall.
>
> BUG=622400
>
> Committed: https://crrev.com/4606ada249a240e115a08a7c66409e8fdd457ea1
> Committed: https://crrev.com/8fd22217395d50b6704109c7f1d4deff59f9a109
> Cr-Original-Commit-Position: refs/heads/master@{#432913}
> Cr-Commit-Position: refs/heads/master@{#433237}

TBR=gab@chromium.org,brettw@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=622400

Committed: https://crrev.com/47c895a15251dde93c04721480cc9f1172d52cca
Cr-Commit-Position: refs/heads/master@{#433267}
==========

[commit-bot: I haz the power, 2016-11-18 19:40:18]

Patchset 1 (id:??) landed as
https://crrev.com/47c895a15251dde93c04721480cc9f1172d52cca
Cr-Commit-Position: refs/heads/master@{#433267}