mash: Fix a mash_browser_tests crash on x11.

mash: Fix a mash_browser_tests crash on x11.

When running as a mus-client, chrome receives from mus, and not from x11.
So the X11EventSource instance is not created.

BUG=594600
Committed: https://crrev.com/53b25adab2383775bffb34a2c5e266b6375898de
Cr-Commit-Position: refs/heads/master@{#395094}

[sadrul, 2016-05-20 15:27:39]

sadrul@chromium.org changed reviewers:
+ sky@chromium.org

[sky, 2016-05-20 16:30:15]

LGTM

[sadrul, 2016-05-20 16:31:49]

The CQ bit was checked by sadrul@chromium.org

[commit-bot: I haz the power, 2016-05-20 16:32:08]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1996413002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1996413002/1

[commit-bot: I haz the power, 2016-05-20 16:36:35]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-05-20 16:38:22]

Description was changed from

==========
mash: Fix a mash_browser_tests crash on x11.

When running as a mus-client, chrome receives from mus, and not from x11.
So the X11EventSource instance is not created.

BUG=594600
==========

to

==========
mash: Fix a mash_browser_tests crash on x11.

When running as a mus-client, chrome receives from mus, and not from x11.
So the X11EventSource instance is not created.

BUG=594600

Committed: https://crrev.com/53b25adab2383775bffb34a2c5e266b6375898de
Cr-Commit-Position: refs/heads/master@{#395094}
==========

[commit-bot: I haz the power, 2016-05-20 16:38:23]

Patchset 1 (id:??) landed as
https://crrev.com/53b25adab2383775bffb34a2c5e266b6375898de
Cr-Commit-Position: refs/heads/master@{#395094}