Turn back spoken feedback setting into a system-wide (non-per-user) preference

Turn back spoken feedback setting into a system-wide (non-per-user) preference 

This patch makes the spoken feedback pref system-wide. As result of it, the device has only one local (non-syncable) preference and all screens (login, user and lock screens) share it. Any user can change it unless the policy doesn't prohibit it.

And this patch also makes the 'DeviceLoginScreenDefaultSpokenFeedbackEnabled' policy deprecated, because we use the same pref store on all screens including lock screen, so we don't need the login-screen specific setting.

BUG=320890
TEST=manually tested on lumpy and chromeos_linux, browsertest/unittest pass.

[yoshiki, 2014-01-16 14:34:40]

achuith@ - Please review chrome/browser/chromeos/preferences.h/.cc. This patch
makes pref::kSpokenFeedback system-wide.

dmazzoni@ - Please review accessibility_manager.cc/.h/_browsertest.cc. This
patch makes the spoken feedback settings system-wide, and fixes the bug in lock
screen (L529 and L871-876 in the original accessibility_manager.cc)

mnissier@ - Please review chrome/browser/chromeos/policy/*. I don't know well
the code about policy. This patch makes the spoken feedback settings system-wide
and removes the 'DeviceLoginScreenDefaultSpokenFeedbackEnabled' policy.

dconnelly@ - Please review policy_templates.json. 
This patch makes the spoken feedback settings per-profile=False and makes the
'DeviceLoginScreenDefaultSpokenFeedbackEnabled' policy depreciated.

[yoshiki, 2014-01-16 14:37:44]

+dtseng@ - Since dmazzoni@ seems ooo now, could you take a look at
accessibility_manager.cc/.h/_browsertest.cc? Thanks.

[achuithb, 2014-01-16 22:46:57]

lgtm for c/b/cros/preferences.*

[dconnelly, 2014-01-17 11:05:34]

https://codereview.chromium.org/136633005/diff/570001/components/policy/resou...
File components/policy/resources/policy_templates.json (right):

https://codereview.chromium.org/136633005/diff/570001/components/policy/resou...
components/policy/resources/policy_templates.json:5346: If you set this policy,
users can temporarily override it by enabling or disabling spoken feedback.
However, the user's choice is not persistent and the default is restored
whenever the login screen is shown anew or the user remains idle on the login
screen for a minute.
Please update the text here as it's no longer per-profile.

https://codereview.chromium.org/136633005/diff/570001/components/policy/resou...
components/policy/resources/policy_templates.json:5348: If this policy is left
unset, spoken feedback is disabled when the login screen is first shown. Users
can enable or disable spoken feedback anytime and its status on the login screen
is persisted between users.''',
Please update the text here as it's no longer per-profile.

[Mattias Nissler (ping if slow), 2014-01-17 12:37:22]

Bartosz should take a look at this as well, since he implemented the policy
pieces.

https://codereview.chromium.org/136633005/diff/570001/chrome/browser/policy/c...
File chrome/browser/policy/configuration_policy_handler_list_factory.cc (left):

https://codereview.chromium.org/136633005/diff/570001/chrome/browser/policy/c...
chrome/browser/policy/configuration_policy_handler_list_factory.cc:424:
base::Value::TYPE_BOOLEAN },
I don't think removing the policy is a good idea, since that means policy can no
longer set a value for the login screen.

[bartfab (slow), 2014-01-17 12:54:31]

On 2014/01/17 12:37:22, Mattias Nissler wrote:
> Bartosz should take a look at this as well, since he implemented the policy
> pieces.
> 
>
https://codereview.chromium.org/136633005/diff/570001/chrome/browser/policy/c...
> File chrome/browser/policy/configuration_policy_handler_list_factory.cc
(left):
> 
>
https://codereview.chromium.org/136633005/diff/570001/chrome/browser/policy/c...
> chrome/browser/policy/configuration_policy_handler_list_factory.cc:424:
> base::Value::TYPE_BOOLEAN },
> I don't think removing the policy is a good idea, since that means policy can
no
> longer set a value for the login screen.

I understand the reason for turning this back into a per-device setting. But the
current implementation won't quite work: For kiosk-type deployments, we need a
way for things to return to a default configuration whenever a user logs out and
the device returns to the login screen. This is what the login screen policy
does right now. We need to maintain this functionality.