[base] Drop obsolete Thread::YieldCPU.

[base] Drop obsolete Thread::YieldCPU.

The method is not used anywhere, and it is a bad idea in general anyway.
If you see a need to call YieldCPU, then you're code is probably in need
of a redesign!

R=svenpanne@chromium.org

Committed: https://crrev.com/cf420ec337e47bed2c754d4ebdc87e8d1bb3cfe5
Cr-Commit-Position: refs/heads/master@{#28147}

[Benedikt Meurer, 2015-04-30 05:00:22]

Hey Sven,

This should be self explanatory. Please take a look.

Thanks,
Benedikt

[Sven Panne, 2015-04-30 08:06:41]

The CQ bit was checked by svenpanne@chromium.org

[Sven Panne, 2015-04-30 08:06:42]

lgtm

[commit-bot: I haz the power, 2015-04-30 08:07:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1116853002/20001

[commit-bot: I haz the power, 2015-04-30 08:08:52]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-30 08:09:05]

Patchset 2 (id:??) landed as
https://crrev.com/cf420ec337e47bed2c754d4ebdc87e8d1bb3cfe5
Cr-Commit-Position: refs/heads/master@{#28147}