mojo: Re-allow empty callbacks to be passed to the bindings.

mojo: Re-allow empty callbacks to be passed to the bindings.

mojo::Callback just ignored null callbacks. Transitioning to
base::Callback, which crashes on null callbacks, caused crashes in some
compositor components.

BUG=620840
Committed: https://crrev.com/97aa5fec3372fc8b658a007e095d614b91893622
Cr-Commit-Position: refs/heads/master@{#400789}

[Elliot Glaysher, 2016-06-20 20:40:39]

erg@chromium.org changed reviewers:
+ yzshen@chromium.org

[yzshen1, 2016-06-20 20:44:10]

The CQ bit was checked by yzshen@chromium.org

[yzshen1, 2016-06-20 20:44:11]

lgtm

[commit-bot: I haz the power, 2016-06-20 20:44:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2084703002/1

[commit-bot: I haz the power, 2016-06-20 21:35:17]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-06-20 21:39:56]

Description was changed from

==========
mojo: Re-allow empty callbacks to be passed to the bindings.

mojo::Callback just ignored null callbacks. Transitioning to
base::Callback, which crashes on null callbacks, caused crashes in some
compositor components.

BUG=620840
==========

to

==========
mojo: Re-allow empty callbacks to be passed to the bindings.

mojo::Callback just ignored null callbacks. Transitioning to
base::Callback, which crashes on null callbacks, caused crashes in some
compositor components.

BUG=620840

Committed: https://crrev.com/97aa5fec3372fc8b658a007e095d614b91893622
Cr-Commit-Position: refs/heads/master@{#400789}
==========

[commit-bot: I haz the power, 2016-06-20 21:39:56]

Patchset 1 (id:??) landed as
https://crrev.com/97aa5fec3372fc8b658a007e095d614b91893622
Cr-Commit-Position: refs/heads/master@{#400789}