ui: Cleanup class/struct forward declarations

content/browser/renderer_host/media/media_devices_manager.h

Index: content/browser/renderer_host/media/media_devices_manager.h
diff --git a/content/browser/renderer_host/media/media_devices_manager.h b/content/browser/renderer_host/media/media_devices_manager.h
index 9610acbbaa7f47a940a9ffb0f8167a236cb50ed5..63b0040959f7bedf4693ce79d0ac9a0cc76c3c7b 100644
--- a/content/browser/renderer_host/media/media_devices_manager.h
+++ b/content/browser/renderer_host/media/media_devices_manager.h
@@ -29,6 +29,18 @@ class VideoCaptureManager;
 using MediaDeviceEnumeration =
     std::array<MediaDeviceInfoArray, NUM_MEDIA_DEVICE_TYPES>;
 
+// MediaDeviceChangeSubscriber is an interface to be implemented by classes
+// that can register with MediaDevicesManager to get notifications about changes
+// in the set of media devices.
+class CONTENT_EXPORT MediaDeviceChangeSubscriber {
+ public:
+  // This function is invoked to notify about changes in the set of media
+  // devices of type |type|. |device_infos| contains the updated list of
+  // devices of type |type|.
+  virtual void OnDevicesChanged(MediaDeviceType type,
+                                const MediaDeviceInfoArray& device_infos) = 0;
+};
+
 // MediaDevicesManager is responsible for doing media-device enumerations.
 // In addition it implements caching for enumeration results and device
 // monitoring in order to keep caches consistent.
@@ -63,6 +75,22 @@ class CONTENT_EXPORT MediaDevicesManager
   void EnumerateDevices(const BoolDeviceTypes& requested_types,
                         const EnumerationCallback& callback);
 
+  // Subscribes |subscriber| to receive device-change notifications for devices
+  // of type |type|. If |subscriber| is already subscribed, this function has
+  // no side effects. MediaDevicesManager does not own |subscriber|. It is the
+  // responsibility of the caller to ensure that all registered subscribers
+  // remain valid while the they are subscribed.
+  void SubscribeDeviceChangeNotifications(
+      MediaDeviceType type,
+      MediaDeviceChangeSubscriber* subscriber);
+
+  // Unubscribes |subscriber| from device-change notifications for the devices
+  // of type |type|. If |subscriber| is not subscribed, this function has no
+  // side effects.
+  void UnsubscribeDeviceChangeNotifications(
+      MediaDeviceType type,
+      MediaDeviceChangeSubscriber* subscriber);
+
   // Tries to start device monitoring. If successful, enables caching of
   // enumeration results for the device types supported by the monitor.
   void StartMonitoring();
@@ -145,6 +173,9 @@ class CONTENT_EXPORT MediaDevicesManager
   MediaDeviceEnumeration current_snapshot_;
   bool monitoring_started_;
 
+  std::vector<MediaDeviceChangeSubscriber*>
+      device_change_subscribers_[NUM_MEDIA_DEVICE_TYPES];
+
   base::WeakPtrFactory<MediaDevicesManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaDevicesManager);