Move all geofencing code into its own module separate from geolocation.

Source/modules/geofencing/Geofencing.idl

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 [
+    NoInterfaceObject,
     RuntimeEnabled=Geofencing,
-    NoInterfaceObject,
     GarbageCollected,
-] interface GeofencingRegion {
-    readonly attribute DOMString id;
+] interface Geofencing {
+    [CallWith=ScriptState] Promise registerRegion(GeofencingRegion region);
+    [CallWith=ScriptState] Promise unregisterRegion(DOMString regionId);
+    [CallWith=ScriptState] Promise getRegisteredRegions();
 };