[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/media_route.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_ROUTE_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTE_H_
 
 #include <string>
 
 #include "base/gtest_prod_util.h"
 #include "base/logging.h"
 #include "base/values.h"
 #include "chrome/browser/media/router/media_route_id.h"
 #include "chrome/browser/media/router/media_sink.h"
 #include "chrome/browser/media/router/media_source.h"
 #include "url/gurl.h"
 
 namespace media_router {
 
 using RouteRequestId = int64;
-
-class MediaRouteFactory;
+const RouteRequestId kInvalidRouteRequestId = -1;
 
 // For now, a simple transition graph: NEW -> CONNECTED -> CLOSED.
 enum MediaRouteState {
   // The route is new and not yet connected to a sink.
   MEDIA_ROUTE_STATE_NEW,
   // The route is active and connected to a sink.
   MEDIA_ROUTE_STATE_CONNECTED,
   // The route has been disconnected.
   MEDIA_ROUTE_STATE_CLOSED
 };
 
 // MediaRoute objects contain the status and metadata of a routing
 // operation. The fields are immutable and reflect the route status
 // only at the time of object creation. Updated route statuses must
 // be retrieved as new MediaRoute objects from the Media Router.
 class MediaRoute {
  public:
   // |media_route_id|: ID of the route. New route IDs should be created
   //                   by the RouteIdManager class.
   // |media_source|: Description of source of the route.
   // |media_sink|: The sink that is receiving the media.
   // |description|: Description of the route to be displayed.
   // |is_local|: true if the route was created from this browser.
   MediaRoute(const MediaRouteId& media_route_id,
              const MediaSource& media_source,
              const MediaSink& media_sink,
              const std::string& description,
              bool is_local);
 
+  // Constructs an empty route. Typically we use an empty MediaRoute rather
+  // than nullptr in situations where route is absent.

[xhwang, 2015/04/02 17:13:02]

What's the use case for this? Personally I feel nullptr is more clear and more
efficient.

[imcheng, 2015/04/02 23:05:23]

Reverted back to nullptr. Since a MediaRoute contains a few other objects, it
feels a bit wasteful to contruct an empty instance.

+  MediaRoute();
+
   ~MediaRoute();
 
+  bool Empty() const;
+
   // The media route identifier.
   const MediaRouteId& media_route_id() const { return media_route_id_; }
 
   // The state of the media route.
   MediaRouteState state() const { return state_; }
 
   // The media source being routed.
   const MediaSource& media_source() const { return media_source_; }
 
   // The sink being routed to.
   const MediaSink& media_sink() const { return media_sink_; }
 
   // The description of the media route activity, for example
   // "Playing Foo Bar Music All Access."
   // TODO(kmarshall): Do we need to pass locale for bidi rendering?
   const std::string& description() const { return description_; }
 
   // Returns |true| if the route is created locally (versus discovered
   // by a media route provider.)
   bool is_local() const { return is_local_; }
 
   bool Equals(const MediaRoute& other) const;
 
  private:
-  const MediaRouteId media_route_id_;
-  const MediaSource media_source_;
-  const MediaSink media_sink_;
-  const std::string description_;
-  const bool is_local_;
-  const MediaRouteState state_;
+  MediaRouteId media_route_id_;
+  MediaSource media_source_;
+  MediaSink media_sink_;
+  std::string description_;
+  bool is_local_;
+  MediaRouteState state_;
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTE_H_