Revert of Refactor FakeAttachmentStore

Revert of Refactor FakeAttachmentStore (patchset #3 id:40001 of https://codereview.chromium.org/601553004/)

Reason for revert:
Speculative revert:
looks like it causes failures on the Linux asan: http://build.chromium.org/p/chromium.memory/builders/Linux%20ASan%20LSan%20Tests%20%283%29/builds/8113

Original issue's description:
> Refactor FakeAttachmentStore
>
> Refactor FakeAttachmentStore into AttachmentStoreProxy and
> InMemoryAttachmentStore backend. Break AttachmentStore interface into
> AttachmentStoreBase (common interface for backends) and AttachmentStore
> (referenced by datatype and AttachmentService).
>
> BUG=
> R=maniscalco@chromium.org
>
> Committed: https://crrev.com/6ae2b341c73909cf902078446346d6c900273409
> Cr-Commit-Position: refs/heads/master@{#297339}

TBR=maniscalco@chromium.org,pavely@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=

Committed: https://crrev.com/198e717d6d35439d59c71519910e7b14c56f8282
Cr-Commit-Position: refs/heads/master@{#297379}

[sergeyv, 2014-09-30 07:47:11]

Created Revert of Refactor FakeAttachmentStore

[commit-bot: I haz the power, 2014-09-30 07:48:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/619563002/1

[commit-bot: I haz the power, 2014-09-30 07:48:50]

Committed patchset #1 (id:1) as 4584be1e64e5a07181fe931203953163986cc8b4

[commit-bot: I haz the power, 2014-09-30 07:50:39]

Patchset 1 (id:??) landed as
https://crrev.com/198e717d6d35439d59c71519910e7b14c56f8282
Cr-Commit-Position: refs/heads/master@{#297379}