Document UMA histograms for app launcher discoverability.

Document UMA histograms for app launcher discoverability.

To track effectiveness of the app launcher install education pages in
enabling users to find, and start using, the app launcher when it is
auto-enabled upon installing the first v2 packaged app from the Web
Store.

Histogram recording committed in http://crrev.com/250348.

BUG=314235
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=251254

[tapted, 2014-02-11 05:25:34]

Hi Alexei, could you take a look at this histograms.xml change? It's been a
while since my last UMA patch - didn't realise we could do these together now
(cool!). Link to the metrics recording code in the linked revision is here: 
https://codereview.chromium.org/143683004/diff/760001/chrome/browser/ui/app_l...

Thanks

[Alexei Svitkine (slow), 2014-02-11 15:43:45]

https://codereview.chromium.org/156963005/diff/1/tools/metrics/histograms/his...
File tools/metrics/histograms/histograms.xml (right):

https://codereview.chromium.org/156963005/diff/1/tools/metrics/histograms/his...
tools/metrics/histograms/histograms.xml:200: +  <summary>The trigger that caused
the app list to be enabled.</summary>
Please expand description to make it clear when this is logged (e.g. is it
logged when app list becomes enabled or is it logged at startup for startups
where app list is on?).

https://codereview.chromium.org/156963005/diff/1/tools/metrics/histograms/his...
tools/metrics/histograms/histograms.xml:217: +<histogram
name="Apps.AppListTimeToDiscover" units="seconds">
Per the client code, the units will not be seconds, since you're logging the
time delta directly. I believe the way you're logging it now, it will be
milliseconds.

[tapted, 2014-02-12 22:51:21]

PTAL

finally got rietveld to accept the patch set... I think. It's being super buggy,
and the updates keep disappearing. 

Direct links seem to work. E.g.
https://codereview.chromium.org/156963005/diff/150001/tools/metrics/histogram...

Otherwise, I've also uploaded to a new issue -- crrev.com/161793002 -- in case
this one is shonky.

https://codereview.chromium.org/156963005/diff/1/tools/metrics/histograms/his...
File tools/metrics/histograms/histograms.xml (right):

https://codereview.chromium.org/156963005/diff/1/tools/metrics/histograms/his...
tools/metrics/histograms/histograms.xml:200: +  <summary>The trigger that caused
the app list to be enabled.</summary>
On 2014/02/11 15:43:46, Alexei Svitkine wrote:
> Please expand description to make it clear when this is logged (e.g. is it
> logged when app list becomes enabled or is it logged at startup for startups
> where app list is on?).

Done.

https://codereview.chromium.org/156963005/diff/1/tools/metrics/histograms/his...
tools/metrics/histograms/histograms.xml:217: +<histogram
name="Apps.AppListTimeToDiscover" units="seconds">
On 2014/02/11 15:43:46, Alexei Svitkine wrote:
> Per the client code, the units will not be seconds, since you're logging the
> time delta directly. I believe the way you're logging it now, it will be
> milliseconds.

Done. +double-checked with --v=1.

Thanks for checking - I had actually assumed this was just a formatting guide,
since FactoryTimeGet only took TimeDelta (i.e. specifying `milliseconds` would
just drop zeros when displaying the histogram, still keeping the raw data
unchanged).

[Alexei Svitkine (slow), 2014-02-13 16:03:26]

thank you, lgtm

[tapted, 2014-02-14 00:29:59]

The CQ bit was checked by tapted@chromium.org

[commit-bot: I haz the power, 2014-02-14 00:32:44]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tapted@chromium.org/156963005/220001

[commit-bot: I haz the power, 2014-02-14 01:10:27]

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

[commit-bot: I haz the power, 2014-02-14 01:10:27]

Retried try job too often on win_rel for step(s) app_list_unittests,
ash_unittests, aura_unittests, cacheinvalidation_unittests, cc_unittests,
check_deps, check_deps2git, chrome_elf_unittests, chromedriver_unittests,
components_unittests, compositor_unittests, content_browsertests,
content_unittests, crypto_unittests, events_unittests, google_apis_unittests,
gpu_unittests, installer_util_unittests, ipc_tests, jingle_unittests,
media_unittests, mini_installer_test, nacl_integration, ppapi_unittests,
printing_unittests, remoting_unittests, sql_unittests, sync_integration_tests,
sync_unit_tests, telemetry_perf_unittests, telemetry_unittests, views_unittests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[tapted, 2014-02-14 01:31:43]

The CQ bit was checked by tapted@chromium.org

[commit-bot: I haz the power, 2014-02-14 01:34:01]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tapted@chromium.org/156963005/220001

[commit-bot: I haz the power, 2014-02-14 04:14:33]

Change committed as 251254