Fix a comment.

Fix a comment.

Optimization: 2 is /O2, not /Os.  (The old comment contradicted the comments
in the FavorSizeOrSpeed section further below.)

BUG=none

Committed: https://crrev.com/3304835477f0f480eff8baadc49c1eb114c451aa
Cr-Commit-Position: refs/heads/master@{#321435}

[Nico, 2015-03-19 19:54:08]

thakis@chromium.org changed reviewers:
+ scottmg@chromium.org

[scottmg, 2015-03-19 20:42:39]

lgtm

[Nico, 2015-03-19 20:43:39]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2015-03-19 20:43:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1020943002/1

[commit-bot: I haz the power, 2015-03-19 21:39:47]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-19 21:40:28]

Patchset 1 (id:??) landed as
https://crrev.com/3304835477f0f480eff8baadc49c1eb114c451aa
Cr-Commit-Position: refs/heads/master@{#321435}