[Media Router] Support dual discovery

chrome/common/media_router/discovery/media_sink_service.h

Index: chrome/common/media_router/discovery/media_sink_service.h
diff --git a/chrome/common/media_router/discovery/media_sink_service.h b/chrome/common/media_router/discovery/media_sink_service.h
index 0fb11b5b8e5e659a02edbef26d2a63c0b5a46396..e510f005d0a68775accd9ab98f82ebec2a95c1d3 100644
--- a/chrome/common/media_router/discovery/media_sink_service.h
+++ b/chrome/common/media_router/discovery/media_sink_service.h
@@ -21,6 +21,15 @@ namespace media_router {
 // 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 =
@@ -39,6 +48,14 @@ class MediaSinkService {
   // 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_;