Fix build error with XCode6/OSX 10.9 SDK

Fix build error with XCode6/OSX 10.9 SDK

OpenGL/gl.h is required to be included to make the build pass.

BUG=
TEST=

Committed: https://crrev.com/cdb1b2d2060234d2a7a766e373a5ffcefce75016
Cr-Commit-Position: refs/heads/master@{#292810}

[Shouqun, 2014-08-29 03:08:20]

Patchset #1 (id:1) has been deleted

[Shouqun, 2014-08-29 04:29:51]

shouqun@chromium.org changed reviewers:
+ miu@chromium.org

[miu, 2014-08-29 05:32:06]

miu@chromium.org changed reviewers:
+ ccameron@chromium.org
- miu@chromium.org

[miu, 2014-08-29 05:33:21]

On 2014/08/29 05:32:06, miu wrote:
> mailto:miu@chromium.org changed reviewers:
> + mailto:ccameron@chromium.org
> - mailto:miu@chromium.org

ccameron@ would know better than me on this.  That, and you'll need his OWNERS
approval anyway.

[ccameron, 2014-08-29 07:32:35]

This seems reasonable (as long as the 10.6 builds still work). That said, I've
moved the file in https://codereview.chromium.org/490393002/, so you'll need to
re-resolve (sorry! ... assuming this actually lands this time)

[ccameron, 2014-08-29 07:32:59]

(and lgtm)

[Shouqun, 2014-08-31 00:39:14]

The CQ bit was checked by shouqun@chromium.org

[commit-bot: I haz the power, 2014-08-31 00:40:11]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/shouqun@chromium.org/522533002/20001

[commit-bot: I haz the power, 2014-08-31 01:36:06]

Committed patchset #1 (id:20001) as b323dce0c209ad5fe76334d86d36dd114d0f8dc1

[commit-bot: I haz the power, 2014-09-10 03:14:54]

Patchset 1 (id:??) landed as
https://crrev.com/cdb1b2d2060234d2a7a766e373a5ffcefce75016
Cr-Commit-Position: refs/heads/master@{#292810}