Hooks together Geolocation Feature in the Client and Engine.

device/geolocation/location_arbitrator_impl.h

Index: device/geolocation/location_arbitrator_impl.h
diff --git a/device/geolocation/location_arbitrator_impl.h b/device/geolocation/location_arbitrator_impl.h
index 9bd5b62e3c98ae99dc28257141386c07e35dc5ca..3ee501409ddf33e22062f0b092952bae0d18661e 100644
--- a/device/geolocation/location_arbitrator_impl.h
+++ b/device/geolocation/location_arbitrator_impl.h
@@ -52,6 +52,8 @@ class DEVICE_GEOLOCATION_EXPORT LocationArbitratorImpl
   bool HasPermissionBeenGrantedForTest() const;
 
   // LocationProvider implementation.
+  // SetUpdateCallback in this case will indicate what callback to pass to each

[Kevin M, 2016/08/19 17:51:37]

I don't think this is the case? Shouldn't the arbitrator be passing its own
internal callback to |providers_|, aggregating the result into a single value,
and then returning that value via |callback|?

[CJ, 2016/08/19 20:44:01]

It is doing that. However, by making LocationArbitrator a LocationProvider, it
gained this function. It's kinda of a case of okay, now that we have this
function what to do with it. Maybe it would best if it was left unimplemented
for LocationArbitrator. 

+  // LocationProvider contained in |providers_|.

[Wez, 2016/08/19 23:12:10]

I'm not sure what this comment means - are you saying that |callback| gets pass
as-is to every provider, or do we still wrap it in some way?

Fundamentally though that's an implementation detail - it's not important to the
caller what happens internally so long as they get the behaviour they expect.

[CJ, 2016/08/22 20:28:08]

The comment on this function no longer applies with the changes that occurred in
GeolocationFeature CL. The behavior is now as expected. Before it was a little
funky, but it got fixed. 

   void SetUpdateCallback(
       const LocationProviderUpdateCallback& callback) override;
   bool StartProvider(bool enable_high_accuracy) override;