Fix signed-compare error with gcc 4.9.2.

Fix signed-compare error with gcc 4.9.2.

From 41f3e782d968.

BUG=

Committed: https://crrev.com/0bc51ef6208b4c98e51ba726c9ea974c206e66d0
Cr-Commit-Position: refs/heads/master@{#31807}

[paul.l..., 2015-11-04 19:24:04]

The CQ bit was checked by paul.lind@imgtec.com to run a CQ dry run

[commit-bot: I haz the power, 2015-11-04 19:24:09]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1431843002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1431843002/1

[paul.l..., 2015-11-04 19:24:59]

paul.lind@imgtec.com changed reviewers:
+ akos.palfi@imgtec.com, rmcilroy@chromium.org

[paul.l..., 2015-11-04 19:24:59]

PTAL.

[commit-bot: I haz the power, 2015-11-04 19:42:34]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-11-04 19:42:35]

Dry run: This issue passed the CQ dry run.

[rmcilroy, 2015-11-04 21:42:18]

lgtm

[paul.l..., 2015-11-04 22:04:37]

The CQ bit was checked by paul.lind@imgtec.com

[commit-bot: I haz the power, 2015-11-04 22:04:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1431843002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1431843002/1

[commit-bot: I haz the power, 2015-11-04 22:06:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-04 22:07:00]

Patchset 1 (id:??) landed as
https://crrev.com/0bc51ef6208b4c98e51ba726c9ea974c206e66d0
Cr-Commit-Position: refs/heads/master@{#31807}