base/threading: remove ScopedTracker placed for experiments

base/threading: remove ScopedTracker placed for experiments

Now that it turns out jank doesn't matter here, let's remove
the experimental code to measure the jank.

BUG=495097
Committed: https://crrev.com/16beb4ed3de2131c961201a5c359462550e83496
Cr-Commit-Position: refs/heads/master@{#341975}

[Takashi Toyoshima, 2015-08-05 05:44:59]

toyoshim@chromium.org changed reviewers:
+ thestig@chromium.org

[Takashi Toyoshima, 2015-08-05 05:47:34]

Hi, let me remove the code for experiments.
It's 0.008 ms in average, and the number hasn't changed before and after the
thread creation change. That means there are no real usages that call
GetThreadId() just after a thread creation in the production.

[Lei Zhang, 2015-08-05 19:42:37]

The CQ bit was checked by thestig@chromium.org

[Lei Zhang, 2015-08-05 19:42:38]

lgtm

[commit-bot: I haz the power, 2015-08-05 19:43:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1265583003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1265583003/1

[commit-bot: I haz the power, 2015-08-05 21:18:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-05 21:19:27]

Patchset 1 (id:??) landed as
https://crrev.com/16beb4ed3de2131c961201a5c359462550e83496
Cr-Commit-Position: refs/heads/master@{#341975}