[Presentation API] Add support for multiple URLs in PresentationRequest on Media Router UI side

chrome/browser/media/router/media_sink.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_SINK_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SINK_H_
 
 #include <string>
 
 namespace media_router {
@@ skipping 26 matching lines @@
   }
   const std::string& description() const { return description_; }
   void set_domain(const std::string& domain) {
     domain_ = domain;
   }
   const std::string& domain() const { return domain_; }
   IconType icon_type() const { return icon_type_; }
 
   bool Equals(const MediaSink& other) const;
 
+  // For storing in sets and in maps as keys.
+  struct Compare {
+    bool operator()(const MediaSink& sink1, const MediaSink& sink2) const {
+      return sink1.id() < sink2.id();
+    }
+  };
+
  private:
   // Unique identifier for the MediaSink.
   MediaSink::Id sink_id_;
 
   // Descriptive name of the MediaSink.
   std::string name_;
 
   // Optional description of the MediaSink.
   std::string description_;
 
   // Optional domain of the MediaSink.
   std::string domain_;
 
   // The type of icon that corresponds with the MediaSink.
   IconType icon_type_;
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SINK_H_