Have WebGeolocationController always wrap up its private controller object

Until Oilpan is firmly enabled, always use GeolocationControllerPrivate
to wrap up the non-owned GeolocationController* object. The previous
implementation was performing an untidy downcast with undefined behavior;
no need for such shortcuts here.

R=
BUG=581112

Review URL: https://codereview.chromium.org/1638573002

Cr-Commit-Position: refs/heads/master@{#371341}
1 file changed