Revert of Abstract //content-level dependencies out of InMemoryURLIndex

Revert of Abstract //content-level dependencies out of InMemoryURLIndex (patchset #5 id:100001 of https://codereview.chromium.org/1186103002/)

Reason for revert:
Speculative revert to fix the Windows unit_test failures.

Original issue's description:
> Abstract //content-level dependencies out of InMemoryURLIndex
>
> It now takes a base::SequencedWorkerPool and a set of client schemes to
> whitelist in its constructor.
>
> BUG=371538
>
> TBR=phajdan.jr
>
> Committed: https://crrev.com/a6da40f8abbf44f8dab8db59a425b85c1db44376
> Cr-Commit-Position: refs/heads/master@{#334799}

TBR=pkasting@chromium.org,phajdan.jr@chromium.org,blundell@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=371538
Committed: https://crrev.com/9d9c3c5655eff730578dc1e9524139ccd60fdb98
Cr-Commit-Position: refs/heads/master@{#334866}

[paulmeyer, 2015-06-17 17:23:18]

Created Revert of Abstract //content-level dependencies out of InMemoryURLIndex

[commit-bot: I haz the power, 2015-06-17 17:23:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1184923006/1

[commit-bot: I haz the power, 2015-06-17 17:25:25]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-17 17:26:22]

Patchset 1 (id:??) landed as
https://crrev.com/9d9c3c5655eff730578dc1e9524139ccd60fdb98
Cr-Commit-Position: refs/heads/master@{#334866}

[paulmeyer, 2015-06-17 18:02:09]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1181353003/ by paulmeyer@chromium.org.

The reason for reverting is: This revert broke other things. Reverting the
revert..