Revert of Implement lossy pref behavior for JsonPrefStore.

Revert of Implement lossy pref behavior for JsonPrefStore. (patchset #12 id:220001 of https://codereview.chromium.org/1127963002/)

Reason for revert:
Linux Valgrind & MSan bot went red due to use of an uninitialized value (newly added POD member missing from second constructor.)

http://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20Tests%20%28valgrind%29%283%29/builds/45675

Original issue's description:
> Implement lossy pref behavior for JsonPrefStore.
>
> Writes to lossy prefs should not trigger writes to disk to be scheduled.
> This behavior is implemented for JsonPrefStore. CommitPendingWrites will
> ensure that all outstanding lossy writes are also written to disk.
>
> BUG=476800
>
> Committed: https://crrev.com/e9d8c9882ca272c803711e26ded4dd7d5203a59e
> Cr-Commit-Position: refs/heads/master@{#329122}

TBR=mnissler@chromium.org,raymes@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=476800
Committed: https://crrev.com/74bb4ded177e5058878ae3d0e510ef83595f8f3a
Cr-Commit-Position: refs/heads/master@{#329169}

[robert.bradford, 2015-05-11 17:14:34]

Created Revert of Implement lossy pref behavior for JsonPrefStore.

[commit-bot: I haz the power, 2015-05-11 17:16:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1136983004/1

[commit-bot: I haz the power, 2015-05-11 17:33:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-11 17:35:45]

Patchset 1 (id:??) landed as
https://crrev.com/74bb4ded177e5058878ae3d0e510ef83595f8f3a
Cr-Commit-Position: refs/heads/master@{#329169}