[Media Router] Convert MediaRouter to use GURL for presentation URLs.

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"
 
+class GURL;
+
+// 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();
 
   // Gets the ID of the media source.
   MediaSource::Id id() const;
 
   // Returns true if two MediaSource objects use the same media ID.
   bool operator==(const MediaSource& other) const;
 
   // Used for logging.
   std::string ToString() const;
 
   // Hash operator for hash containers.
   struct Hash {
     size_t operator()(const MediaSource& source) const {
       return base::Hash(source.id());
     }
   };
 
  private:
   MediaSource::Id id_;
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SOURCE_H_