Fix number of buckets in Tabs.ScrubDistance UMA histogram.

Fix number of buckets in Tabs.ScrubDistance UMA histogram.

Fix the number of buckets in Tabs.ScrubDistance. Currently the value
19 falls in the bucket with value 18 which is confusing. Results can be
checked on uma.googleplex.com.

BUG=

Committed: https://crrev.com/f7d782116910dc7d962c245e0ccac2a5feefa6cc
Cr-Commit-Position: refs/heads/master@{#296957}

[timvolodine, 2014-09-08 16:08:05]

timvolodine@chromium.org changed reviewers:
+ davemoore@chromium.org, lliabraa@chromium.org

[DaveMoore, 2014-09-09 14:31:25]

lgtm

[timvolodine, 2014-09-15 12:04:21]

timvolodine@chromium.org changed reviewers:
+ derat@chromium.org

[timvolodine, 2014-09-15 12:04:22]

+ derat@ as OWNER

[Daniel Erat, 2014-09-15 14:35:36]

lgtm

[timvolodine, 2014-09-26 15:43:39]

The CQ bit was checked by timvolodine@chromium.org

[commit-bot: I haz the power, 2014-09-26 15:44:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/551893002/1

[commit-bot: I haz the power, 2014-09-26 16:21:33]

Committed patchset #1 (id:1) as 24c62d250b6c84a4dceda88193a5dec63f298384

[commit-bot: I haz the power, 2014-09-26 16:22:23]

Patchset 1 (id:??) landed as
https://crrev.com/f7d782116910dc7d962c245e0ccac2a5feefa6cc
Cr-Commit-Position: refs/heads/master@{#296957}