Revert of Use TaskScheduler instead of SequencedWorkerPool in snapshot_cache.mm.

Revert of Use TaskScheduler instead of SequencedWorkerPool in snapshot_cache.mm. (patchset #2 id:20001 of https://codereview.chromium.org/2881873002/ )

Reason for revert:
Probably this CL causes many failures of iOS bots. For example, https://build.chromium.org/p/chromium.mac/builders/ios-simulator/builds/17573

Original issue's description:
> Use TaskScheduler instead of SequencedWorkerPool in snapshot_cache.mm.
> 
> SequencedWorkerPool is being deprecated in favor of TaskScheduler.
> 
> BUG=667892
> R=jif@chromium.org
> 
> Review-Url: https://codereview.chromium.org/2881873002
> Cr-Commit-Position: refs/heads/master@{#472052}
> Committed: https://chromium.googlesource.com/chromium/src/+/aa5299ae23a57ca5dce00a11da3ac8e73849351f

TBR=jif@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=667892
Review-Url: https://codereview.chromium.org/2889553002
Cr-Commit-Position: refs/heads/master@{#472065}
Committed: https://chromium.googlesource.com/chromium/src/+/fb580dd729ddfbd6729c8ba416f8b6f2d474a44b

[kolos1, 2017-05-16 12:19:39]

The CQ bit was checked by kolos@chromium.org

[kolos1, 2017-05-16 12:19:40]

Created Revert of Use TaskScheduler instead of SequencedWorkerPool in
snapshot_cache.mm.

[commit-bot: I haz the power, 2017-05-16 12:19:59]

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, 2017-05-16 12:20:18]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1494937179772100, "parent_rev":
"3b7bbdee66154192e114f69457e411fcce7333a9", "commit_rev":
"fb580dd729ddfbd6729c8ba416f8b6f2d474a44b"}

[commit-bot: I haz the power, 2017-05-16 12:20:29]

Description was changed from

==========
Revert of Use TaskScheduler instead of SequencedWorkerPool in snapshot_cache.mm.
(patchset #2 id:20001 of https://codereview.chromium.org/2881873002/ )

Reason for revert:
Probably this CL causes many failures of iOS bots. For example,
https://build.chromium.org/p/chromium.mac/builders/ios-simulator/builds/17573

Original issue's description:
> Use TaskScheduler instead of SequencedWorkerPool in snapshot_cache.mm.
> 
> SequencedWorkerPool is being deprecated in favor of TaskScheduler.
> 
> BUG=667892
> R=jif@chromium.org
> 
> Review-Url: https://codereview.chromium.org/2881873002
> Cr-Commit-Position: refs/heads/master@{#472052}
> Committed:
https://chromium.googlesource.com/chromium/src/+/aa5299ae23a57ca5dce00a11da3a...

TBR=jif@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=667892
==========

to

==========
Revert of Use TaskScheduler instead of SequencedWorkerPool in snapshot_cache.mm.
(patchset #2 id:20001 of https://codereview.chromium.org/2881873002/ )

Reason for revert:
Probably this CL causes many failures of iOS bots. For example,
https://build.chromium.org/p/chromium.mac/builders/ios-simulator/builds/17573

Original issue's description:
> Use TaskScheduler instead of SequencedWorkerPool in snapshot_cache.mm.
> 
> SequencedWorkerPool is being deprecated in favor of TaskScheduler.
> 
> BUG=667892
> R=jif@chromium.org
> 
> Review-Url: https://codereview.chromium.org/2881873002
> Cr-Commit-Position: refs/heads/master@{#472052}
> Committed:
https://chromium.googlesource.com/chromium/src/+/aa5299ae23a57ca5dce00a11da3a...

TBR=jif@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=667892

Review-Url: https://codereview.chromium.org/2889553002
Cr-Commit-Position: refs/heads/master@{#472065}
Committed:
https://chromium.googlesource.com/chromium/src/+/fb580dd729ddfbd6729c8ba416f8...
==========

[commit-bot: I haz the power, 2017-05-16 12:20:30]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/fb580dd729ddfbd6729c8ba416f8...