[MediaRouter] Add implementation of PresentationServiceDelegate

chrome/browser/media/router/presentation_media_sinks_observer.h

 // Copyright 2015 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_BROWSER_MEDIA_ROUTER_PRESENTATION_MEDIA_SINKS_OBSERVER_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_PRESENTATION_MEDIA_SINKS_OBSERVER_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/media/router/media_sinks_observer.h"
@@ skipping 19 matching lines @@
   // Does not take ownership of |listener| or |router|.
   PresentationMediaSinksObserver(
       MediaRouter* router,
       content::PresentationScreenAvailabilityListener* listener,
       const MediaSource& source);
   ~PresentationMediaSinksObserver() override;
 
   // MediaSinksObserver implementation.
   void OnSinksReceived(const std::vector<MediaSink>& result) override;
 
+  content::PresentationScreenAvailabilityListener* listener() const {
+    return listener_;
+  }
+
  private:
   enum Availability { UNKNOWN, AVAILABLE, UNAVAILABLE };
 
   content::PresentationScreenAvailabilityListener* listener_;
   Availability previous_availablity_;
 
   DISALLOW_COPY_AND_ASSIGN(PresentationMediaSinksObserver);
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_PRESENTATION_MEDIA_SINKS_OBSERVER_H_