Revert of Fire an alert event to notify accessibility when a permissions bubble gets shown.

Revert of Fire an alert event to notify accessibility when a permissions bubble gets shown. (patchset #6 id:100001 of https://codereview.chromium.org/1055883002/)

Reason for revert:
Not lg'ed by OWNER as of latest patchset.

Original issue's description:
> Add an event to notify accessibility when a permissions bubble gets shown.
>
> BUG=381338
> TEST=ctrl+alt+z; navigate to html5demos.com/geo; observe speech is as expected (reads contents of bubble).
>
> Committed: https://crrev.com/36318aa45e02cf0b5cf871bf38bbe47f3431cc8d
> Cr-Commit-Position: refs/heads/master@{#323982}

TBR=felt@chromium.org,markusheintz@chromium.org,dmazzoni@chromium.org,msw@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=381338
Committed: https://crrev.com/449dc46f27b0deb7ed813d718c2aa88f23838f70
Cr-Commit-Position: refs/heads/master@{#324060}

[David Tseng, 2015-04-07 16:59:53]

Created Revert of Fire an alert event to notify accessibility when a permissions
bubble gets shown.

[commit-bot: I haz the power, 2015-04-07 17:00:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1066973002/1

[commit-bot: I haz the power, 2015-04-07 17:01:22]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-07 17:03:21]

Patchset 1 (id:??) landed as
https://crrev.com/449dc46f27b0deb7ed813d718c2aa88f23838f70
Cr-Commit-Position: refs/heads/master@{#324060}

[msw, 2015-04-07 19:53:28]

lgtm, re-landing with some explanatory comments is probably sufficient as a
first-pass. Thanks for filing http://crbug.com/474622