[Extensions] Make handler_function a hidden property

[Extensions] Make handler_function a hidden property

Fix the glitch and add a test.

BUG=548273
Committed: https://crrev.com/a5ecbc86a598e29ce3a2424c9c5386bfba4e9b74
Cr-Commit-Position: refs/heads/master@{#356985}

[Devlin, 2015-10-29 20:45:26]

Description was changed from

==========
crbug.com/548273
BUG=
==========

to

==========
[Extensions] Make handler_function a hidden property

Fix the glitch and add a test.

BUG=548273
==========

[Devlin, 2015-10-29 20:48:38]

Patchset #2 (id:20001) has been deleted

[Devlin, 2015-10-29 22:59:05]

rdevlin.cronin@chromium.org changed reviewers:
+ jochen@chromium.org

[jochen (gone - plz use gerrit), 2015-10-29 23:03:36]

lgtm

[Devlin, 2015-10-29 23:04:07]

The CQ bit was checked by rdevlin.cronin@chromium.org

[commit-bot: I haz the power, 2015-10-29 23:07:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1422383003/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1422383003/40001

[commit-bot: I haz the power, 2015-10-29 23:41:38]

Committed patchset #2 (id:40001)

[commit-bot: I haz the power, 2015-10-29 23:42:39]

Patchset 2 (id:??) landed as
https://crrev.com/a5ecbc86a598e29ce3a2424c9c5386bfba4e9b74
Cr-Commit-Position: refs/heads/master@{#356985}