[Media Router] Support dual discovery

chrome/common/media_router/discovery/media_sink_service.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_COMMON_MEDIA_ROUTER_DISCOVERY_MEDIA_SINK_SERVICE_H_
 #define CHROME_COMMON_MEDIA_ROUTER_DISCOVERY_MEDIA_SINK_SERVICE_H_
 
 #include <memory>
 #include <vector>
 
 #include "base/callback.h"
 #include "chrome/common/media_router/discovery/media_sink_internal.h"
 #include "chrome/common/media_router/media_sink.h"
 
 namespace media_router {
 
 // A service which can be used to start background discovery and resolution of
 // MediaSinks. Often these are remote devices, like Chromecast. In addition, the
 // service is capable of answering MediaSink queries using the sinks that it
 // generated.
 // This class is not thread safe. All methods must be called from the UI thread.
 class MediaSinkService {
  public:
+  class Observer {
+   public:
+    // Invoked when |sink| is added to current service.
+    virtual void OnMediaSinkAdded(const MediaSinkInternal& sink) = 0;
+
+    // Invoked when media sinks are removed from current service.
+    virtual void OnMediaSinksRemoved() = 0;
+  };
+
   // Callback to be invoked when this class finishes sink discovering.
   // Arg 0: Sinks discovered and resolved by the service.
   using OnSinksDiscoveredCallback =
       base::Callback<void(std::vector<MediaSinkInternal>)>;
 
   explicit MediaSinkService(
       const OnSinksDiscoveredCallback& sink_discovery_callback);
 
   virtual ~MediaSinkService();
 
   // Starts sink discovery. No-ops if already started.
   // Sinks discovered and resolved are continuously passed to
   // |callback|.
   virtual void Start() = 0;
 
   // Stops sink discovery. No-ops if already stopped.
   virtual void Stop() = 0;
 
+  // Adds |observer| to current service. Does not take ownership of |observer|.
+  // Caller should make sure that |observer| outlives current service.
+  virtual void AddObserver(Observer* observer) = 0;
+
+  // Removes |observer| from current service. Does not take ownership of
+  // |observer|.
+  virtual void RemoveObserver(Observer* observer) = 0;
+
  protected:
   OnSinksDiscoveredCallback sink_discovery_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaSinkService);
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_COMMON_MEDIA_ROUTER_DISCOVERY_MEDIA_SINK_SERVICE_H_