Make Menu.findMenuItem_ return the first MenuItem.

Make Menu.findMenuItem_ return the first MenuItem.

This fixes the regression in http://crbug.com/480381 where 'activate'
event is not fired for menu items under a grouping div rather than
being direct children of a Menu. Also fixes js error when hovering
such menu items.

BUG=480381
Committed: https://crrev.com/95a989fc01c61f3261b1b9723efab0b0c6be56a3
Cr-Commit-Position: refs/heads/master@{#327080}

[xiyuan, 2015-04-23 20:46:34]

xiyuan@chromium.org changed reviewers:
+ dbeam@chromium.org

[Dan Beam, 2015-04-23 21:33:01]

dbeam@chromium.org changed reviewers:
+ arv@chromium.org
- dbeam@chromium.org

[Dan Beam, 2015-04-23 21:33:01]

this seems fine to me but arv@ is probably a better reviewer for this

[arv (Not doing code reviews), 2015-04-27 17:34:15]

LGTM

This seems fine to me.

[xiyuan, 2015-04-27 17:34:34]

On 2015/04/27 17:34:15, arv wrote:
> LGTM
> 
> This seems fine to me.

Cool. Thanks.

[xiyuan, 2015-04-27 17:34:49]

The CQ bit was checked by xiyuan@chromium.org

[commit-bot: I haz the power, 2015-04-27 17:35:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1095303004/1

[commit-bot: I haz the power, 2015-04-27 18:31:18]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-27 18:33:06]

Patchset 1 (id:??) landed as
https://crrev.com/95a989fc01c61f3261b1b9723efab0b0c6be56a3
Cr-Commit-Position: refs/heads/master@{#327080}