Claim MPArch.* process management metrics.

Claim MPArch.* process management metrics.

This patch sets ppi@ as owner of histograms tracking the child process
launch time (important as this is a significant performance factor on
some platforms) and number of renderer processes kept around.

BUG=401821
Committed: https://crrev.com/eb340f90bc01d6ce3fc7df2d95cc2954ea256b45
Cr-Commit-Position: refs/heads/master@{#291918}

[ppi, 2014-08-26 14:35:09]

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

[ppi, 2014-08-26 14:35:09]

Hi Alexei, ptal.

[Alexei Svitkine (slow), 2014-08-26 14:51:05]

The CQ bit was checked by asvitkine@chromium.org

[Alexei Svitkine (slow), 2014-08-26 14:51:06]

lgtm

[commit-bot: I haz the power, 2014-08-26 14:51:42]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ppi@chromium.org/500403002/1

[commit-bot: I haz the power, 2014-08-26 15:47:10]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_gpu_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu_triggered...)
  win_chromium_x64_rel_swarming on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[commit-bot: I haz the power, 2014-08-26 16:29:58]

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

[commit-bot: I haz the power, 2014-08-26 16:29:59]

Failed to commit the patch.

[ppi, 2014-08-26 16:47:54]

The CQ bit was checked by ppi@chromium.org

[commit-bot: I haz the power, 2014-08-26 16:49:10]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ppi@chromium.org/500403002/1

[commit-bot: I haz the power, 2014-08-26 16:50:21]

Committed patchset #1 (1) as 3710ac7153ce182cefea53b207903993c4bd7fdd

[commit-bot: I haz the power, 2014-09-10 02:43:18]

Patchset 1 (id:??) landed as
https://crrev.com/eb340f90bc01d6ce3fc7df2d95cc2954ea256b45
Cr-Commit-Position: refs/heads/master@{#291918}