Change MenuControllerDelegate to provide WeakPtr

Change MenuControllerDelegate to provide WeakPtr

So it is possible that a MenuControllerDelegate can be destroyed in a fashion
which does not notify the associated MenuController. This can leak to the
controller attempting to access the delegate after death.

Specifically a MenuControllerDelegate, which does not own the controller is
closed. Then at some point later on released as its Widgets are cleaned up.

The MenuController is then further interacted with, beginning to show another
menu.

Then at some point the MenuController is finally shutdown. Notifying all
associated delegates.

This change updates MenuControllerDelegate to provide a WeakPtr. MenuController
will verify existance before notifying delegates of shutdown.

TEST=MenuRunnerImplTest.NestedDelegateDestroyedWhileMenuRunning
BUG=683087

[jonross, 2017-01-27 16:23:25]

The CQ bit was checked by jonross@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-01-27 16:23:50]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[jonross, 2017-01-27 16:25:05]

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

[jonross, 2017-01-27 16:25:05]

Hey sky@,

This is a follow up to yesterday's review. There is apparently a way for
MenuRunnerImpl to die without any notification to the MenuController.

Could you review this change?

Thanks,
Jon

[commit-bot: I haz the power, 2017-01-27 17:14:04]

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

[commit-bot: I haz the power, 2017-01-27 17:14:05]

Dry run: This issue passed the CQ dry run.