[Media Router] Convert to use typemaps for media_router.mojom.

chrome/browser/media/router/media_source.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_MEDIA_SOURCE_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SOURCE_H_
 
 #include <stddef.h>
 
 #include <ostream>
 #include <string>
 
 #include "base/hash.h"
 #include "url/gurl.h"
 
 // TODO(mfoltz): Right now this is a wrapper for std::string.  Factor methods
 // from media_source_helper here so this object becomes useful; and don't just
 // pass it around by Id.
 namespace media_router {
 
 class MediaSource {
  public:
   using Id = std::string;
 
   explicit MediaSource(const MediaSource::Id& id);
   explicit MediaSource(const GURL& presentation_url);
+  MediaSource();
   ~MediaSource();
 
   // Gets the ID of the media source.
   MediaSource::Id id() const;
 
   // If MediaSource is created from a URL, return the URL; otherwise return an
   // empty GURL.
   GURL url() const;
 
   // Returns true if two MediaSource objects use the same media ID.
@@ skipping 10 matching lines @@
   };
 
  private:
   MediaSource::Id id_;
   GURL url_;
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SOURCE_H_