Revert of Reland of "Remove void** from disk_cache interface."

Revert of Reland of "Remove void** from disk_cache interface." (patchset #2 id:40001 of https://codereview.chromium.org/583283002/)

Reason for revert:
Suspected for causing accessibility tests to flake.

Original issue's description:
> Reland of "Remove void** from disk_cache interface."
>
> Enumeration and iteration were passing around void**. With this CL, we
> instead use an Iterator object.
>
> TBR=clamy@chromium.org,jkarlin@chromium.org,jsbell@chromium.org
> BUG=413644
>
> Committed: https://crrev.com/edbfba945a76d97383122a01529abfe3ce63d34d
> Cr-Commit-Position: refs/heads/master@{#295870}

TBR=clamy@chromium.org,jkarlin@chromium.org,jsbell@chromium.org,rvargas@chromium.org,gavinp@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=413644
Committed: https://crrev.com/ac2c408b1930266531c0c3c4ad429c0652e4748a
Cr-Commit-Position: refs/heads/master@{#295887}

[dcheng, 2014-09-20 19:46:35]

Created Revert of Reland of "Remove void** from disk_cache interface."

[commit-bot: I haz the power, 2014-09-20 19:47:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/592503002/1

[commit-bot: I haz the power, 2014-09-20 19:47:46]

Committed patchset #1 (id:1) as 3d22dec2ffd5937676e8184d3a10f6f48f504763

[commit-bot: I haz the power, 2014-09-20 19:48:15]

Patchset 1 (id:??) landed as
https://crrev.com/ac2c408b1930266531c0c3c4ad429c0652e4748a
Cr-Commit-Position: refs/heads/master@{#295887}