Refactor to make BlimpLocationProvider accessible to content layer.

content/browser/geolocation/location_arbitrator_impl.h

Index: content/browser/geolocation/location_arbitrator_impl.h
diff --git a/content/browser/geolocation/location_arbitrator_impl.h b/content/browser/geolocation/location_arbitrator_impl.h
index 60c9ac57a905d817611ca6e92531187aaa508083..0320689b8dc1b66e56f51db9f035e4cdb3fcedab 100644
--- a/content/browser/geolocation/location_arbitrator_impl.h
+++ b/content/browser/geolocation/location_arbitrator_impl.h
@@ -8,6 +8,7 @@
 #include <stdint.h>
 
 #include "base/callback_forward.h"
+#include "base/cancelable_callback.h"
 #include "base/macros.h"
 #include "base/memory/scoped_vector.h"
 #include "base/strings/string16.h"
@@ -68,6 +69,10 @@ class CONTENT_EXPORT LocationArbitratorImpl : public LocationArbitrator {
   // Takes ownership of |provider| on entry; it will either be added to
   // |providers_| or deleted on error (e.g. it fails to start).
   void RegisterProvider(LocationProvider* provider);
+
+  // Checks for either an override or a system location provider and
+  // calls RegisterProvider for it.
+  void RegisterSystemProvider();
   void OnAccessTokenStoresLoaded(
       AccessTokenStore::AccessTokenMap access_token_map,
       net::URLRequestContextGetter* context_getter);
@@ -87,6 +92,9 @@ class CONTENT_EXPORT LocationArbitratorImpl : public LocationArbitrator {
   scoped_refptr<AccessTokenStore> access_token_store_;
   LocationUpdateCallback arbitrator_update_callback_;
   LocationProvider::LocationProviderUpdateCallback provider_update_callback_;
+  base::CancelableCallback<void(AccessTokenStore::AccessTokenMap,

[Michael van Ouwerkerk, 2016/06/10 12:46:52]

Why is this cancelable but never cancelled, and why is it stored in the
arbitrator? It seems neither aspect is needed.

[CJ, 2016/06/10 19:51:34]

This was done so the reset method could be used. The arbitrator was doing checks
in the OnAccessTokenStoresLoaded method that were basically doing the
functionality of Reset(), but the checks caused the need for some weird control
flow. 

[Kevin M, 2016/06/10 20:39:11]

To be a little more specific - it's cancelable so that
OnAccessTokenStoresLoaded() only gets called once. The previous implementation
of OnAccessTokenStoresLoaded did something similar in a more roundabout way by
checking whether |providers_| is empty.

[Michael van Ouwerkerk, 2016/06/14 16:46:42]

It would be good to add a little documentation at the usage site to explain why
this is needed (multiple calls).

[Michael van Ouwerkerk, 2016/06/14 16:46:42]

Ah, that's really neat actually. Thanks!

[CJ, 2016/06/21 21:27:41]

Done.

+                                net::URLRequestContextGetter*)>
+      token_store_callback_;
   ScopedVector<LocationProvider> providers_;
   bool enable_high_accuracy_;
   // The provider which supplied the current |position_|