Add Apps.AppListSearchQueryLength UMA histogram.

Add Apps.AppListSearchQueryLength UMA histogram.

This CL adds a histogram to track the length of the app list search query
at the time a result is opened. This will provide information about the
efficiency of users of the app list search.

BUG=485449
Committed: https://crrev.com/6508a61109dad09944bda378b3b6f3874bfa18a4
Cr-Commit-Position: refs/heads/master@{#329299}

[calamity, 2015-05-11 04:08:53]

Patchset #1 (id:1) has been deleted

[calamity, 2015-05-11 04:09:02]

calamity@chromium.org changed reviewers:
+ mgiuca@chromium.org

[Matt Giuca, 2015-05-11 04:27:37]

lgtm, but aren't you adding a bunch of other histos at the same time? Wouldn't
it be worth just doing them all in one CL to avoid having to do many review
cycles with the histograms.xml people?

[calamity, 2015-05-11 06:52:34]

calamity@chromium.org changed reviewers:
+ asvitkine@chromium.org

[calamity, 2015-05-11 06:52:34]

+asvitkine for histograms OWNERS.

[calamity, 2015-05-11 06:53:00]

The CQ bit was checked by calamity@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-05-11 06:54:47]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1128413002/20001

[commit-bot: I haz the power, 2015-05-11 08:07:56]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-05-11 08:07:58]

Dry run: This issue passed the CQ dry run.

[Alexei Svitkine (slow), 2015-05-11 15:01:15]

lgtm

[calamity, 2015-05-12 00:41:56]

The CQ bit was checked by calamity@chromium.org

[commit-bot: I haz the power, 2015-05-12 00:43:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1128413002/20001

[commit-bot: I haz the power, 2015-05-12 00:49:54]

Committed patchset #1 (id:20001)

[commit-bot: I haz the power, 2015-05-12 00:50:44]

Patchset 1 (id:??) landed as
https://crrev.com/6508a61109dad09944bda378b3b6f3874bfa18a4
Cr-Commit-Position: refs/heads/master@{#329299}