ui/gfx: Add exclusion for testing/gmock to DEPS.

ui/gfx: Add exclusion for testing/gmock to DEPS.

This is so we can prevent other from adding this dependency back.

They will think twice or at least consult with OWNERS if we have this in
place in the DEPS exclusion list.

BUG=134675
TEST=checkdeps
R=sky@chromium.org

Committed: https://crrev.com/76ebffc02eb4275a837ae8122bed5628ed44f513
Cr-Commit-Position: refs/heads/master@{#330392}

[sky, 2015-05-18 16:55:47]

LGTM

[tfarina, 2015-05-18 17:02:23]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2015-05-18 17:03:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1138643012/1

[commit-bot: I haz the power, 2015-05-18 20:17:10]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-18 22:41:36]

Patchset 1 (id:??) landed as
https://crrev.com/76ebffc02eb4275a837ae8122bed5628ed44f513
Cr-Commit-Position: refs/heads/master@{#330392}