Revert of [ServiceWorkerCache Cleanup] Make the state of the cache backend explicit

Revert of [ServiceWorkerCache Cleanup] Make the state of the cache backend explicit (patchset #2 id:20001 of https://codereview.chromium.org/701403002/)

Reason for revert:
There is a bad DCHECK causing layout tests to fail.  Reverting and fixing later so that I can turn the tests back on asap as this patch is non-essential and it's branch day.

BUG=431163
Original issue's description:
> [ServiceWorkerCache] Make the state of the cache backend explicit
>
> The ServiceWorkerCache's backend transitions from uninitialized, to
> open, to closed.  Make that explicit in code by adding a state
> variable instead of checking the state of the initialized_ and
> backend_ member variables.
>
> BUG=430884
>
> Committed: https://crrev.com/7fbcce797ed32cf1d653ca5e4bf1dfad4cd7fc46
> Cr-Commit-Position: refs/heads/master@{#303115}

TBR=michaeln@chromium.org,falken@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=430884
Committed: https://crrev.com/0d9168154dea976f5f490666791d3c44e68c9ea6
Cr-Commit-Position: refs/heads/master@{#303226}

[jkarlin, 2014-11-07 12:46:45]

Created Revert of [ServiceWorkerCache Cleanup] Make the state of the cache
backend explicit

[commit-bot: I haz the power, 2014-11-07 12:47:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/709003003/1

[commit-bot: I haz the power, 2014-11-07 12:47:26]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-11-07 12:48:11]

Patchset 1 (id:??) landed as
https://crrev.com/0d9168154dea976f5f490666791d3c44e68c9ea6
Cr-Commit-Position: refs/heads/master@{#303226}