Revert of ServiceWorker: Use SimpleCache for the script cache

Revert of ServiceWorker: Use SimpleCache for the script cache (patchset #7 id:230001 of https://codereview.chromium.org/1140853002/)

Reason for revert:
We'll reland this CL with DiskCache migration code.

Original issue's description:
> ServiceWorker: Use SimpleCache for the script cache
>
> This CL migrates the backend of ServiceWorkerDiskCache from Default to
> SimpleCache on all platforms.
>
> If old DiskCache images exist,
> (1) DiskCache backend fails to open an pre-existing data due to incompatible
> format (in both Default->SimpleCache and SimpleCache->Default cases),
> (2) ServiceWorkerStorage wipes out all cached scripts and registrations via
> DeleteAndStartOver, and
> (3) navigation falls back to network.
>
> BUG=487482
> TEST=manual (use DiskCache and SimpleCache alternately and make sure the system can recover)
>
> Committed: https://crrev.com/a00e5be5a06e626de1b62cbfc7c350bef08647ea
> Cr-Commit-Position: refs/heads/master@{#330274}

TBR=michaeln@chromium.org
BUG=487482
Committed: https://crrev.com/d89b8b3d592ee47b47d5774712bbec541188d114
Cr-Commit-Position: refs/heads/master@{#330505}

[nhiroki, 2015-05-19 09:47:14]

Created Revert of ServiceWorker: Use SimpleCache for the script cache

[nhiroki, 2015-05-19 09:49:34]

kinuko@, can I land this?

[kinuko, 2015-05-19 10:24:37]

lgtm

[nhiroki, 2015-05-19 10:50:43]

The CQ bit was checked by nhiroki@chromium.org

[commit-bot: I haz the power, 2015-05-19 10:50:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1142193002/1

[commit-bot: I haz the power, 2015-05-19 11:38:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-19 11:39:30]

Patchset 1 (id:??) landed as
https://crrev.com/d89b8b3d592ee47b47d5774712bbec541188d114
Cr-Commit-Position: refs/heads/master@{#330505}