Basic implementation of GeofencingManager class.

This class is the single entry point for all Geofencing related API calls, and will be responsible for storing all geofence registrations, and registering them with the underlying platform specific GeofencingProvider.

BUG=383125

Review URL: https://codereview.chromium.org/586163003

Cr-Commit-Position: refs/heads/master@{#299172}
11 files changed