Revert of Add a default task runner argument to the constructor of JsonPrefStore.

Revert of Add a default task runner argument to the constructor of JsonPrefStore. (patchset #3 id:40001 of https://codereview.chromium.org/2876643003/ )

Reason for revert:
Broke compile step on ChromiumOS x86-generic Compile:

https://uberchromegw.corp.google.com/i/chromium.chromiumos/builders/ChromiumOS%20x86-generic%20Compile/builds/35463

Original issue's description:
> Add a default task runner argument to the constructor of JsonPrefStore.
> 
> Callers that don't need to run tasks on the same sequence as the
> JsonPrefStore will be able to use the default argument.
> 
> BUG=667892
> 
> Review-Url: https://codereview.chromium.org/2876643003
> Cr-Commit-Position: refs/heads/master@{#471428}
> Committed: https://chromium.googlesource.com/chromium/src/+/22f197b4c0399140f9cf118136a8c96b8ad8af9a

TBR=gab@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/2884473002
Cr-Commit-Position: refs/heads/master@{#471450}
Committed: https://chromium.googlesource.com/chromium/src/+/1104930da3c75f52ec2c438d01c5b06850beb301

[Justin Donnelly, 2017-05-12 21:40:04]

The CQ bit was checked by jdonnelly@chromium.org

[Justin Donnelly, 2017-05-12 21:40:05]

Created Revert of Add a default task runner argument to the constructor of
JsonPrefStore.

[commit-bot: I haz the power, 2017-05-12 21:41:20]

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, 2017-05-12 21:41:55]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1494625204823480, "parent_rev":
"be738df8f289bf20423865f1bc555f2976a2e921", "commit_rev":
"1104930da3c75f52ec2c438d01c5b06850beb301"}

[commit-bot: I haz the power, 2017-05-12 21:42:07]

Description was changed from

==========
Revert of Add a default task runner argument to the constructor of
JsonPrefStore. (patchset #3 id:40001 of
https://codereview.chromium.org/2876643003/ )

Reason for revert:
Broke compile step on ChromiumOS x86-generic Compile:

https://uberchromegw.corp.google.com/i/chromium.chromiumos/builders/ChromiumO...

Original issue's description:
> Add a default task runner argument to the constructor of JsonPrefStore.
> 
> Callers that don't need to run tasks on the same sequence as the
> JsonPrefStore will be able to use the default argument.
> 
> BUG=667892
> 
> Review-Url: https://codereview.chromium.org/2876643003
> Cr-Commit-Position: refs/heads/master@{#471428}
> Committed:
https://chromium.googlesource.com/chromium/src/+/22f197b4c0399140f9cf118136a8...

TBR=gab@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 Add a default task runner argument to the constructor of
JsonPrefStore. (patchset #3 id:40001 of
https://codereview.chromium.org/2876643003/ )

Reason for revert:
Broke compile step on ChromiumOS x86-generic Compile:

https://uberchromegw.corp.google.com/i/chromium.chromiumos/builders/ChromiumO...

Original issue's description:
> Add a default task runner argument to the constructor of JsonPrefStore.
> 
> Callers that don't need to run tasks on the same sequence as the
> JsonPrefStore will be able to use the default argument.
> 
> BUG=667892
> 
> Review-Url: https://codereview.chromium.org/2876643003
> Cr-Commit-Position: refs/heads/master@{#471428}
> Committed:
https://chromium.googlesource.com/chromium/src/+/22f197b4c0399140f9cf118136a8...

TBR=gab@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/2884473002
Cr-Commit-Position: refs/heads/master@{#471450}
Committed:
https://chromium.googlesource.com/chromium/src/+/1104930da3c75f52ec2c438d01c5...
==========

[commit-bot: I haz the power, 2017-05-12 21:42:08]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/1104930da3c75f52ec2c438d01c5...