[sensors][permission] Add/Register sensor permission types in content_settings.

[sensors][permission] Add/Register in content_settings.

We register the content settings for different sensors.
The policy as suggesed by chrome privacy team is ->

AMBIENT_LIGHT_SENSOR: opt-out UI. granted by default.
MAGNETOMETER: opt-out UI. granted by default.
ORIENTATION_SENSOR: opt-out UI. granted by default.

ACCELEROMETER: auto-grant. no UI.
GYROSCOPE: auto grant. no UI.

BUG=606766

[riju_, 2017-04-04 15:37:53]

rijubrata.bhaumik@intel.com changed reviewers:
+ mlamouri@chromium.org, raymes@chromium.org

[riju_, 2017-04-04 15:37:53]

PTAL. 
This is part 2 of adding permission guard for sensors based on Generic Sensor
API.

Depends on https://codereview.chromium.org/2791623004/

[mlamouri (slow - plz ping), 2017-04-05 13:18:03]

lgtm but please wait for raymes@

[raymes, 2017-04-06 05:39:21]

Hey riju,

The code here is starting to be dependent on what UI surfaces we will have for
these permissions. We should first determine what UI surfaces we are going to
use/build and then we can add new content settings based on that. 

To give an example, we may decide we only expose one setting in the UI for all
types of sensors. If we do that, we would only need one content setting to store
that data.

[raymes, 2017-04-06 05:48:29]

You may want to include a section in the design doc on UI and CC folks like
owencm, benwells, dominickn, emilyschechter.

Thanks!

[shalamov, 2017-04-13 12:33:22]

On 2017/04/06 05:48:29, raymes wrote:
> You may want to include a section in the design doc on UI and CC folks like
> owencm, benwells, dominickn, emilyschechter.
> 
> Thanks!

Added chapter about Chrome UI with mocks
(https://docs.google.com/document/d/1Ml65ZdW5AgIsZTszk4mD_ohr40pcrdVFOIf0ZtWxD...)

CC'd owencm, benwells, dominickn, emilyschechter.