Move the Chrome Variations HTTP header helper file into c/b/metrics/variations, and fix up lock beh…

Move the Chrome Variations HTTP header helper file into c/b/metrics/variations, and fix up lock behavior a bit.

Specifically:
  (1) Reduces the duration for which the lock is held when appending HTTP headers.
  (2) Adds a debug assertion that the lock is correctly held when calling UpdateVariationIDsHeaderValue().

BUG=none

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=175967

[Ilya Sherman, 2013-01-09 05:19:43]

Alexei, WDYT?

[Alexei Svitkine (slow), 2013-01-09 15:30:45]

LGTM! Thanks for the cleanup.

It would have been better to do the slight logic tweak (with the lock) in a
separate CL, though.

[commit-bot: I haz the power, 2013-01-09 15:31:06]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/isherman@chromium.org/11821019/1008

[commit-bot: I haz the power, 2013-01-09 15:31:12]

Presubmit check for 11821019-1008 failed and returned exit status 1.


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Missing LGTM from an OWNER for files in these directories:
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[Ilya Sherman, 2013-01-09 22:28:18]

Nico, mind stamping for chrome/ OWNERS approval?  Thanks.

[Nico, 2013-01-09 22:30:05]

The CL says "fix up lock behavior a little bit" (without any test changes),
which doesn't really conform to cpu@'s please for better changelog messages.

[Ilya Sherman, 2013-01-09 22:51:56]

On 2013/01/09 22:30:05, Nico wrote:
> The CL says "fix up lock behavior a little bit" (without any test changes),
> which doesn't really conform to cpu@'s please for better changelog messages.

No test changes because these are more stylistic issues than functional ones. 
Updated the changelog to be more informative.

[Nico, 2013-01-09 22:52:34]

lgtm stamp

[commit-bot: I haz the power, 2013-01-09 22:53:30]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/isherman@chromium.org/11821019/1008

[commit-bot: I haz the power, 2013-01-10 01:26:10]

Change committed as 175967