Add UMA stat to track usage of Chrome for Linux accross different window managers

Add UMA stat to track usage of Chrome for Linux across different window managers.

Knowing which window managers Chrome is most often used on will help in testing in new feature development.

BUG=372580
TEST=None

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=276593

[pkotwicz, 2014-06-11 17:54:48]

Elliot, can you please take an initial looks before I send it off to isherman@

[Elliot Glaysher, 2014-06-11 19:09:08]

I guess this lg, but I don't know anything about uma stats.

[pkotwicz, 2014-06-11 19:24:38]

Isherman@ can you please take a look?

[Ilya Sherman, 2014-06-11 20:07:56]

LGTM % a comment:

https://codereview.chromium.org/330493002/diff/1/tools/metrics/histograms/his...
File tools/metrics/histograms/histograms.xml (right):

https://codereview.chromium.org/330493002/diff/1/tools/metrics/histograms/his...
tools/metrics/histograms/histograms.xml:9349: +  <summary>The window manager
used. (Linux only)</summary>
Please document when this metric is recorded.

[pkotwicz, 2014-06-11 21:46:31]

The CQ bit was checked by pkotwicz@chromium.org

[commit-bot: I haz the power, 2014-06-11 21:48:36]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/330493002/20001

[commit-bot: I haz the power, 2014-06-11 23:04:28]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  ios_dbg_simulator on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_dbg_simulator/bui...)
  ios_rel_device on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_rel_device/builds...)
  ios_rel_device_ninja on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_rel_device_ninja/...)
  mac_chromium_compile_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_compile_...)
  mac_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_rel/buil...)
  win_chromium_compile_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_compile_...)
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)
  win_chromium_x64_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_x64_rel/...)
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/15688)
  win_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu/builds/18821)

[commit-bot: I haz the power, 2014-06-11 23:06:12]

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

[commit-bot: I haz the power, 2014-06-11 23:06:14]

Try jobs failed on following builders:
  ios_dbg_simulator on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_dbg_simulator/bui...)
  ios_rel_device on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_rel_device/builds...)
  ios_rel_device_ninja on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_rel_device_ninja/...)
  mac_chromium_compile_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_compile_...)
  mac_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_rel/buil...)
  win_chromium_compile_dbg on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_compile_...)
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/15758)
  win_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu/builds/18890)

[pkotwicz, 2014-06-12 01:28:32]

The CQ bit was checked by pkotwicz@chromium.org

[commit-bot: I haz the power, 2014-06-12 01:32:20]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/330493002/20001

[commit-bot: I haz the power, 2014-06-12 09:12:33]

Change committed as 276593