Fix pkg-config issue with cras for Chrome OS build.

Fix pkg-config issue with cras for Chrome OS build.

BUG=None
TEST=Run `gn gen` with 'os="chromeos" use_cras=true'.

Committed: https://crrev.com/77287dc5c9fb6d6a17febdcfb33a792523dca01a
Cr-Commit-Position: refs/heads/master@{#301477}

[Ben Chan, 2014-10-27 20:53:52]

benchan@chromium.org changed reviewers:
+ dalecurtis@chromium.org

[DaleCurtis, 2014-10-27 21:32:03]

lgtm

[Ben Chan, 2014-10-27 21:33:10]

The CQ bit was checked by benchan@chromium.org

[commit-bot: I haz the power, 2014-10-27 21:37:08]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/682743003/1

[commit-bot: I haz the power, 2014-10-27 23:19:25]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-27 23:20:07]

Patchset 1 (id:??) landed as
https://crrev.com/77287dc5c9fb6d6a17febdcfb33a792523dca01a
Cr-Commit-Position: refs/heads/master@{#301477}