Avoid a string copy for every CommandLine::HasSwitch query

Avoid a string copy for every CommandLine::HasSwitch query

Windows performs a lower-case conversion of all strings passed to
CommandLine::HasSwitch. Other platforms require no such conversion,
however, currently they pay for an associated string copy on each query.
Why? Because compilers aren't as smart as they should be. Remove this
string copy for non-Windows platforms. A string copy saved is a string
copy earned.

BUG=405348
Committed: https://crrev.com/034cff8362b7fe30be88b9e344544be486bae74c
Cr-Commit-Position: refs/heads/master@{#308839}

[jdduke (slow), 2014-12-17 17:51:47]

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

[jdduke (slow), 2014-12-17 17:51:48]

thestig@: PTAL. I was surprised, but both GCC/Clang aren't smart enough to elide
the string copy here. This cuts the cost of each query by 1/3 (from 1.8us to
1.2us, which admittedly isn't huge, but these queries can definitely be on the
fast path =/).

[Lei Zhang, 2014-12-17 19:17:41]

lgtm

[jdduke (slow), 2014-12-17 19:19:12]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2014-12-17 19:20:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/815543002/20001

[commit-bot: I haz the power, 2014-12-17 19:35:25]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-12-17 19:36:15]

Patchset 2 (id:??) landed as
https://crrev.com/034cff8362b7fe30be88b9e344544be486bae74c
Cr-Commit-Position: refs/heads/master@{#308839}