Replace base::CallbackList with base::ObserverList in CastConfigDelegate

ash/cast_config_delegate.h

Index: ash/cast_config_delegate.h
diff --git a/ash/cast_config_delegate.h b/ash/cast_config_delegate.h
index 9c1e1c6b379e9e2312bcf3d1497ea8708c992480..dd6be59dfa058412a1d103b6afdcce93f8dcc8ea 100644
--- a/ash/cast_config_delegate.h
+++ b/ash/cast_config_delegate.h
@@ -10,7 +10,6 @@
 
 #include "ash/ash_export.h"
 #include "base/callback.h"
-#include "base/callback_list.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string16.h"
@@ -71,12 +70,13 @@ class CastConfigDelegate {
     Activity activity;
   };
 
-  // The key is the receiver id.
   using ReceiversAndActivities = std::vector<ReceiverAndActivity>;
-  using ReceiversAndActivitesCallback =
-      base::Callback<void(const ReceiversAndActivities&)>;
-  using DeviceUpdateSubscription = scoped_ptr<
-      base::CallbackList<void(const ReceiversAndActivities&)>::Subscription>;
+
+  class Observer {
+   public:
+    // Invoked whenever there is new receiver or activity information available.
+    virtual void OnDevicesUpdated(const ReceiversAndActivities& devices);
+  };
 

[stevenjb, 2016/01/12 23:31:49]

Typically an observer class with only one or two methods should be a pure
virtual with no default implementations. (I'm actually surprised this didn't
generate a link error).

Also, all virtual classes need an explicit destructor (which can be inlined if
it is a pure virtual class).

[jdufault, 2016/01/12 23:59:22]

Done.

   virtual ~CastConfigDelegate() {}
 
@@ -85,10 +85,9 @@ class CastConfigDelegate {
   // gone. See crbug.com/551132.
   virtual bool HasCastExtension() const = 0;
 
-  // Adds a listener that will get invoked whenever the receivers or their
-  // associated activites have changed.
-  virtual DeviceUpdateSubscription RegisterDeviceUpdateObserver(
-      const ReceiversAndActivitesCallback& callback) = 0;
+  // Add or remove an observer.
+  virtual void AddObserver(Observer* observer) = 0;
+  virtual void RemoveObserver(Observer* observer) = 0;
 
   // Request fresh data from the backend. When the data is available, all
   // registered observers will get called.