Add a callback for cancelling the context menu.

Add a callback for cancelling the context menu.

The callback updates the |visible| property to NO so clients can
correctly determine if the context menu has been dismissed.

BUG=489121
Committed: https://crrev.com/1f113f3df1edef7c130691e5a36b65b95ff95eff
Cr-Commit-Position: refs/heads/master@{#330562}

[lliabraa, 2015-05-19 13:12:13]

lliabraa@chromium.org changed reviewers:
+ eugenebut@chromium.org

[Eugene But (OOO till 7-30), 2015-05-19 16:56:27]

lgtm

[lliabraa, 2015-05-19 17:05:14]

The CQ bit was checked by lliabraa@chromium.org

[commit-bot: I haz the power, 2015-05-19 17:09:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1144873002/1

[commit-bot: I haz the power, 2015-05-19 17:20:30]

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

[commit-bot: I haz the power, 2015-05-19 17:20:32]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[lliabraa, 2015-05-19 17:50:01]

lliabraa@chromium.org changed reviewers:
+ rohitrao@chromium.org

[lliabraa, 2015-05-19 17:50:01]

+rohitrao for OWNERS

[rohitrao (ping after 24h), 2015-05-19 17:59:27]

lgtm!

[lliabraa, 2015-05-19 18:14:54]

The CQ bit was checked by lliabraa@chromium.org

[commit-bot: I haz the power, 2015-05-19 18:16:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1144873002/1

[commit-bot: I haz the power, 2015-05-19 18:20:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-19 18:22:43]

Patchset 1 (id:??) landed as
https://crrev.com/1f113f3df1edef7c130691e5a36b65b95ff95eff
Cr-Commit-Position: refs/heads/master@{#330562}