[Device Discovery] Make DialRegistry a Singleton

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

 // Copyright (c) 2012 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_EXTENSIONS_API_DIAL_DIAL_API_H_
 #define CHROME_BROWSER_EXTENSIONS_API_DIAL_DIAL_API_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 74 matching lines @@
   // listeners.
   void NotifyListenerAddedOnIOThread();
   void NotifyListenerRemovedOnIOThread();
 
   // Fills the |device| API struct from |device_data|.
   void FillDialDevice(const media_router::DialDeviceData& device_data,
                       api::dial::DialDevice* device) const;
 
   Profile* profile_;
 
-  // Created lazily on first access on the IO thread.
-  std::unique_ptr<media_router::DialRegistry> dial_registry_;
+  // Created lazily on first access on the IO thread. Does not take ownership of
+  // |dial_registry_|.
+  media_router::DialRegistry* dial_registry_;
 
   // Device data for testing.
   std::unique_ptr<media_router::DialDeviceData> test_device_data_;
   std::unique_ptr<media_router::DialDeviceDescriptionData>
       test_device_description_;
 
   DISALLOW_COPY_AND_ASSIGN(DialAPI);
 };
 
 // DiscoverNow function. This function needs a round-trip from the IO thread
@@ skipping 50 matching lines @@
       device_description_fetcher_;
 
   DialAPI* dial_;
 
   DISALLOW_COPY_AND_ASSIGN(DialFetchDeviceDescriptionFunction);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_DIAL_DIAL_API_H_