IndexedDB: Re-enable leveldb manifest reuse.

IndexedDB: Re-enable leveldb manifest reuse.

The new leveldb manifest reuse feature was disabled because the CrOS dev channel
daily error % by channel values increased after this landed in that channel (by
about 3x). Reverting this change did not return the dev channel rates back to
normal. Furthermore the beta channel (with this feature enabled) did not
experience an increase in errors.

Commit details: Returns manifest reuse back to the state introduced in
crrev.com/803603004 (de701ab) which was disabled in two subsequent reverts:
crrev.com/841753003 (ca6c875) and crrev.com/852073002 (617e94e).

BUG=402980
Committed: https://crrev.com/6bd2fc1919a84eff0141634ccc49483669ab7e37
Cr-Commit-Position: refs/heads/master@{#314638}

[cmumford, 2015-02-04 18:46:42]

cmumford@chromium.org changed reviewers:
+ dgrogan@chromium.org, michaeln@chromium.org

[dgrogan, 2015-02-04 19:21:07]

Is the plan still to fully enable on the 41 beta branch instead of its current
murky state and, in parallel, run a 50/50 experiment on 42?

[cmumford, 2015-02-04 19:31:02]

On 2015/02/04 19:21:07, dgrogan wrote:
> Is the plan still to fully enable on the 41 beta branch instead of its current
> murky state and, in parallel, run a 50/50 experiment on 42?

yep - I'll get guidance from the finch team as to the sample population size.

[dgrogan, 2015-02-04 20:01:54]

lgtm

[cmumford, 2015-02-04 20:13:59]

The CQ bit was checked by cmumford@chromium.org

[commit-bot: I haz the power, 2015-02-04 20:15:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/899933002/1

[michaeln, 2015-02-04 20:15:43]

lgtm 2, great to see this going back in!

[commit-bot: I haz the power, 2015-02-04 21:24:20]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-04 21:25:26]

Patchset 1 (id:??) landed as
https://crrev.com/6bd2fc1919a84eff0141634ccc49483669ab7e37
Cr-Commit-Position: refs/heads/master@{#314638}