[Dial] Refactor DialRegistry and DeviceDescriptionFetcher so they can be used by MediaSinkService

chrome/browser/extensions/api/dial/dial_registry.h

Index: chrome/browser/extensions/api/dial/dial_registry.h
diff --git a/chrome/browser/extensions/api/dial/dial_registry.h b/chrome/browser/extensions/api/dial/dial_registry.h
index e43d207bff830aa3fbecae52d6ea9a674cc9cc01..b193b833439c9c589f9b9c5a54188653df994902 100644
--- a/chrome/browser/extensions/api/dial/dial_registry.h
+++ b/chrome/browser/extensions/api/dial/dial_registry.h
@@ -16,6 +16,7 @@
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/observer_list.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "chrome/browser/extensions/api/dial/dial_service.h"
@@ -57,8 +58,7 @@ class DialRegistry : public DialService::Observer,
 
   // Create the DIAL registry and pass a reference to allow it to notify on
   // DIAL device events.
-  DialRegistry(Observer* dial_api,
-               const base::TimeDelta& refresh_interval,
+  DialRegistry(const base::TimeDelta& refresh_interval,

[imcheng, 2017/03/06 20:56:30]

base::TimeDelta is small enough that usually it is passed by value instead of
const ref.

[zhaobin, 2017/03/07 00:13:18]

Done.

                const base::TimeDelta& expiration,
                const size_t max_devices);
 
@@ -70,6 +70,10 @@ class DialRegistry : public DialService::Observer,
   void OnListenerAdded();
   void OnListenerRemoved();
 
+  // This class does not take ownership of observer.
+  void RegisterObserver(Observer* observer);
+  void UnregisterObserver(Observer* observer);
+
   // Called by the DIAL API to try to kickoff a discovery if there is not one
   // already active.
   bool DiscoverNow();
@@ -111,6 +115,10 @@ class DialRegistry : public DialService::Observer,
   void OnNetworkChanged(
       net::NetworkChangeNotifier::ConnectionType type) override;
 
+  // Notify all observers about DialDeviceEvent or DialError.
+  void OnDialDeviceEvent(const DeviceList& devices);
+  void OnDialError(DialErrorCode type);
+
   // Starts and stops periodic discovery.  Periodic discovery is done when there
   // are registered event listeners.
   void StartPeriodicDiscovery();
@@ -178,7 +186,7 @@ class DialRegistry : public DialService::Observer,
 
   // Interface from which the DIAL API is notified of DIAL device events. the
   // DIAL API owns this DIAL registry.
-  Observer* const dial_api_;
+  base::ObserverList<Observer> observers_;
 
   FRIEND_TEST_ALL_PREFIXES(DialRegistryTest, TestAddRemoveListeners);
   FRIEND_TEST_ALL_PREFIXES(DialRegistryTest, TestNoDevicesDiscovered);