Revert of [Sync] Refactoring polling to be reliable.

Revert of [Sync] Refactoring polling to be reliable. (patchset #5 id:80001 of https://codereview.chromium.org/1132013004/)

Reason for revert:
Failing on valgrind bots

Original issue's description:
> [Sync] Refactoring polling to be reliable.
>
> Polling is now an important component of sync health, as it can sometimes be
> the only time we'll query for certain datatypes. As such, the following
> has changed:
> - Polls that fail will be retried (with backoff).
> - As such, the logic to force a poll after an auth error isn't needed anymore
> - The last successful poll time will be persisted in the sync prefs.
> - On startup, schedule the first poll for last_poll_time + poll_interval
>   (or Now(), whichever is latest).
> - Receiving a new poll interval from the server will update the poll timer
> - The poll timer is now a one shot timer, and only restarts on success
> - Some code cleanup to make the above more straightforward
>
> BUG=482154
>
> Committed: https://crrev.com/3777d8727d7b4caedfb72bfdcbe2fea1f1d1d594
> Cr-Commit-Position: refs/heads/master@{#329669}

TBR=pavely@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=482154
Committed: https://crrev.com/938b3c001b85f2193151dda0ae659ba776d12e1f
Cr-Commit-Position: refs/heads/master@{#329683}

[Nicolas Zea, 2015-05-13 18:44:08]

Created Revert of [Sync] Refactoring polling to be reliable.

[commit-bot: I haz the power, 2015-05-13 18:45:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1144443004/1

[commit-bot: I haz the power, 2015-05-13 18:47:31]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-13 18:48:14]

Patchset 1 (id:??) landed as
https://crrev.com/938b3c001b85f2193151dda0ae659ba776d12e1f
Cr-Commit-Position: refs/heads/master@{#329683}