Namespace clean-up in histogram_tester_unittest.cc

Namespace clean-up in histogram_tester_unittest.cc

This CL introduces an anonymous namespace instead of using "static" for global constants. It is a follow-up to https://codereview.chromium.org/1264123002/.

R=thestig@chromium.org
BUG=473689
Committed: https://crrev.com/3db30f9fa710e97054703cee6909533b5bb0a96c
Cr-Commit-Position: refs/heads/master@{#341732}

[vabr (Chromium), 2015-08-04 10:23:40]

Hi Lei,

PTAL, this is a follow-up to https://codereview.chromium.org/1264123002/#msg18.

Cheers,
Vaclav

[Lei Zhang, 2015-08-04 16:19:20]

The CQ bit was checked by thestig@chromium.org

[Lei Zhang, 2015-08-04 16:19:20]

lgtm

[commit-bot: I haz the power, 2015-08-04 16:19:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1271933002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1271933002/1

[commit-bot: I haz the power, 2015-08-04 16:26:53]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-04 16:27:22]

Patchset 1 (id:??) landed as
https://crrev.com/3db30f9fa710e97054703cee6909533b5bb0a96c
Cr-Commit-Position: refs/heads/master@{#341732}