Updates Geolocation to use a pair of maps to store watchers.

Updates Geolocation to use a pair of maps to store watchers.

This reflects a recent change submitted to webkit.org (see
http://trac.webkit.org/changeset/50159). This came about in the
course of upstreaming the logic to make sure the error callback
is called when permissions have already been denied (see
http://trac.webkit.org/changeset/50190).

Also make some minor style and comment changes to reflect other
recent submissions to webkit.org.

This will avoid future merge conflicts.

Change-Id: Iafca02403b781bc2119e6e762cb04df396ca8c11