Revert of Use TaskScheduler instead of WorkerPool in cache_util.cc.

Revert of Use TaskScheduler instead of WorkerPool in cache_util.cc. (patchset #3 id:40001 of https://codereview.chromium.org/2610503002/ )

Reason for revert:
It looks like this CL may be related to a unit test failure on this build:
https://build.chromium.org/p/chromium.win/builders/Win10%20Tests%20x64/builds/7492
- Sheriff

Original issue's description:
> Use TaskScheduler instead of WorkerPool in cache_util.cc.
> 
> The following traits are used:
> 
> Priority: BACKGROUND
>   User won't notice if this task takes an arbitrarily long time
>   to complete.
> 
> Shutdown behavior: CONTINUE_ON_SHUTDOWN
>   Tasks posted with this mode which have not started executing before
>   shutdown is initiated will never run. Tasks with this mode running at
>   shutdown will be ignored (the worker will not be joined).
> 
>   Note: Tasks that were previously posted to base::WorkerPool should
>   use this shutdown behavior because this is how base::WorkerPool
>   handles all its tasks.
> 
> May Block:
>   Tasks posted with MayBlock() may block. This includes but is not
>   limited to tasks that wait on synchronous file I/O operations:
>   read or write a file from disk, interact with a pipe or a socket,
>   rename or delete a file, enumerate files in a directory, etc. This
>   trait isn't required for the mere use of locks.
> 
> BUG=659191
> 
> Review-Url: https://codereview.chromium.org/2610503002
> Cr-Commit-Position: refs/heads/master@{#442985}
> Committed: https://chromium.googlesource.com/chromium/src/+/8d1a5a1e352ee6b2aee40b42d9fdc4b6e0c97fed

TBR=gavinp@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=659191
Review-Url: https://codereview.chromium.org/2626163002
Cr-Commit-Position: refs/heads/master@{#443009}
Committed: https://chromium.googlesource.com/chromium/src/+/92581e4786c05bd34bdb9cdfa0acb7de669ca6c4

[dschuyler, 2017-01-11 22:12:06]

The CQ bit was checked by dschuyler@chromium.org

[dschuyler, 2017-01-11 22:12:06]

Created Revert of Use TaskScheduler instead of WorkerPool in cache_util.cc.

[commit-bot: I haz the power, 2017-01-11 22:14:09]

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, 2017-01-11 22:16:17]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1484172726186430, "parent_rev":
"273c31e1ab4a2180fbcbe2c1829b2c05717aa50e", "commit_rev":
"92581e4786c05bd34bdb9cdfa0acb7de669ca6c4"}

[commit-bot: I haz the power, 2017-01-11 22:16:50]

Description was changed from

==========
Revert of Use TaskScheduler instead of WorkerPool in cache_util.cc. (patchset #3
id:40001 of https://codereview.chromium.org/2610503002/ )

Reason for revert:
It looks like this CL may be related to a unit test failure on this build:
https://build.chromium.org/p/chromium.win/builders/Win10%20Tests%20x64/builds...
- Sheriff

Original issue's description:
> Use TaskScheduler instead of WorkerPool in cache_util.cc.
> 
> The following traits are used:
> 
> Priority: BACKGROUND
>   User won't notice if this task takes an arbitrarily long time
>   to complete.
> 
> Shutdown behavior: CONTINUE_ON_SHUTDOWN
>   Tasks posted with this mode which have not started executing before
>   shutdown is initiated will never run. Tasks with this mode running at
>   shutdown will be ignored (the worker will not be joined).
> 
>   Note: Tasks that were previously posted to base::WorkerPool should
>   use this shutdown behavior because this is how base::WorkerPool
>   handles all its tasks.
> 
> May Block:
>   Tasks posted with MayBlock() may block. This includes but is not
>   limited to tasks that wait on synchronous file I/O operations:
>   read or write a file from disk, interact with a pipe or a socket,
>   rename or delete a file, enumerate files in a directory, etc. This
>   trait isn't required for the mere use of locks.
> 
> BUG=659191
> 
> Review-Url: https://codereview.chromium.org/2610503002
> Cr-Commit-Position: refs/heads/master@{#442985}
> Committed:
https://chromium.googlesource.com/chromium/src/+/8d1a5a1e352ee6b2aee40b42d9fd...

TBR=gavinp@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=659191
==========

to

==========
Revert of Use TaskScheduler instead of WorkerPool in cache_util.cc. (patchset #3
id:40001 of https://codereview.chromium.org/2610503002/ )

Reason for revert:
It looks like this CL may be related to a unit test failure on this build:
https://build.chromium.org/p/chromium.win/builders/Win10%20Tests%20x64/builds...
- Sheriff

Original issue's description:
> Use TaskScheduler instead of WorkerPool in cache_util.cc.
> 
> The following traits are used:
> 
> Priority: BACKGROUND
>   User won't notice if this task takes an arbitrarily long time
>   to complete.
> 
> Shutdown behavior: CONTINUE_ON_SHUTDOWN
>   Tasks posted with this mode which have not started executing before
>   shutdown is initiated will never run. Tasks with this mode running at
>   shutdown will be ignored (the worker will not be joined).
> 
>   Note: Tasks that were previously posted to base::WorkerPool should
>   use this shutdown behavior because this is how base::WorkerPool
>   handles all its tasks.
> 
> May Block:
>   Tasks posted with MayBlock() may block. This includes but is not
>   limited to tasks that wait on synchronous file I/O operations:
>   read or write a file from disk, interact with a pipe or a socket,
>   rename or delete a file, enumerate files in a directory, etc. This
>   trait isn't required for the mere use of locks.
> 
> BUG=659191
> 
> Review-Url: https://codereview.chromium.org/2610503002
> Cr-Commit-Position: refs/heads/master@{#442985}
> Committed:
https://chromium.googlesource.com/chromium/src/+/8d1a5a1e352ee6b2aee40b42d9fd...

TBR=gavinp@chromium.org,fdoray@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=659191

Review-Url: https://codereview.chromium.org/2626163002
Cr-Commit-Position: refs/heads/master@{#443009}
Committed:
https://chromium.googlesource.com/chromium/src/+/92581e4786c05bd34bdb9cdfa0ac...
==========

[commit-bot: I haz the power, 2017-01-11 22:16:51]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/92581e4786c05bd34bdb9cdfa0ac...