Add the first very basic bits of a geofencing API.

Just adding the various methods on navigator.geolocation, which currently all always fail.

BUG=383125

Review URL: https://codereview.chromium.org/375353002

git-svn-id: svn://svn.chromium.org/blink/trunk@178052 bbb929c8-8fbe-4397-9dbb-9b2b20218538