Fix missing SB2DatabaseFailure histogram entries

Fix missing SB2DatabaseFailure histogram entries

Also fix some mislabelled entries in the histogram enum.

Make the declaration site explicit to decrease the likelihood of such
omissions/mislabels happening again in the future.

BUG=None

Committed: https://crrev.com/71e1f811453fb04379d003d3d92d657e72a2030c
Cr-Commit-Position: refs/heads/master@{#318893}

[gab, 2015-03-02 17:12:22]

gab@chromium.org changed reviewers:
+ asvitkine@chromium.org, mattm@chromium.org

[gab, 2015-03-02 17:13:10]

Matt/Alexei PTAL, fixed issue observed by Alexei @
https://codereview.chromium.org/611603002/diff/340001/chrome/browser/safe_bro...

[Alexei Svitkine (slow), 2015-03-02 17:40:33]

lgtm

[mattm, 2015-03-02 22:32:17]

lgtm

[gab, 2015-03-03 13:11:20]

The CQ bit was checked by gab@chromium.org

[commit-bot: I haz the power, 2015-03-03 13:12:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/968253002/1

[commit-bot: I haz the power, 2015-03-03 16:37:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-03 16:38:21]

Patchset 1 (id:??) landed as
https://crrev.com/71e1f811453fb04379d003d3d92d657e72a2030c
Cr-Commit-Position: refs/heads/master@{#318893}