Add UMA for app list creation time.

Add UMA for app list creation time.

This CL adds a UMA histogram for the amount of time taken to build the
app list.

BUG=415389
Committed: https://crrev.com/a0b19056a6cc3da38b88f6d813f3ac9e1d4af695
Cr-Commit-Position: refs/heads/master@{#295672}

[calamity, 2014-09-18 01:57:51]

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

[Alexei Svitkine (slow), 2014-09-18 17:36:22]

lgtm

[calamity, 2014-09-19 04:20:17]

The CQ bit was checked by calamity@chromium.org

[commit-bot: I haz the power, 2014-09-19 04:20:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/580993003/1

[commit-bot: I haz the power, 2014-09-19 04:23:09]

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

[commit-bot: I haz the power, 2014-09-19 04:23:10]

Try jobs failed on following builders:
  ios_rel_device on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device/bu...)
  mac_chromium_compile_dbg on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)
  win8_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_rel...)

[calamity, 2014-09-19 06:01:30]

Patchset #2 (id:20001) has been deleted

[calamity, 2014-09-19 06:01:41]

The CQ bit was checked by calamity@chromium.org

[commit-bot: I haz the power, 2014-09-19 06:02:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/580993003/40001

[commit-bot: I haz the power, 2014-09-19 06:57:12]

Committed patchset #2 (id:40001) as 20e376b15b43c4fe8098737b1c0009b14ce072f2

[commit-bot: I haz the power, 2014-09-19 06:58:21]

Patchset 2 (id:??) landed as
https://crrev.com/a0b19056a6cc3da38b88f6d813f3ac9e1d4af695
Cr-Commit-Position: refs/heads/master@{#295672}

[calamity, 2014-10-31 05:16:17]

Patchset #3 (id:60001) has been deleted

[calamity, 2014-10-31 05:16:23]

Patchset #3 (id:80001) has been deleted