[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/media_route_response.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_RESPONSE_H_
+#define CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTE_RESPONSE_H_
+
+#include <string>
+
+#include "base/memory/scoped_ptr.h"
+#include "chrome/browser/media/router/media_route.h"
+
+namespace media_router {
+
+// Response to a media route request to the Media Route Provider.
+class MediaRouteResponse {
+ public:
+  // Creates a MediaRouteResponse object that indicates success.
+  // |request_id|: ID of original request.
+  // |route|: Route created.
+  static scoped_ptr<MediaRouteResponse> Success(
+      const RouteRequestId& request_id,
+      const MediaRoute& route);
+  // Creates a MediaRouteResponse object that indicates failure.
+  // |request_id|: ID of original request.
+  // |error|: Failure reason.
+  static scoped_ptr<MediaRouteResponse> Error(const RouteRequestId& request_id,
+                                              const std::string& error);
+
+  ~MediaRouteResponse();
+
+  const RouteRequestId& request_id() const { return request_id_; }
+  // Returns a pointer to the route created. Returns nullptr if response
+  // indicates error.
+  const MediaRoute* route() const { return route_.get(); }

[Kevin M, 2015/03/26 20:50:14]

Return const reference instead? See comment below.

[imcheng, 2015/03/26 23:33:12]

Chatted offline. Done. 

+  const std::string& error() const { return error_; }
+
+ private:
+  MediaRouteResponse(const RouteRequestId& request_id, const MediaRoute& route);
+  MediaRouteResponse(const RouteRequestId& request_id,
+                     const std::string& error);
+  MediaRouteResponse(const MediaRouteResponse& other);
+
+  // ID of original request. Set in all MediaRouteResponse objects, regardless
+  // of success/failure.
+  const RouteRequestId request_id_;
+  // The route created as a result of the request. Points to a valid MediaRoute
+  // iff the response indicates success, nullptr otherwise.
+  const scoped_ptr<MediaRoute> route_;

[Kevin M, 2015/03/26 20:50:14]

How about just putting a MediaRoute here, instead of a pointer to a MediaRoute?

A default empty state would suffice for error cases. You could add
MediaRoute::empty() which would simply check for an empty string route ID.

Then you can return a const MediaRoute& for route(). Passing back references for
getters when possible is safer from a segfault perspective, and more idiomatic.

[imcheng, 2015/03/26 23:33:13]

Done.

+  // Set to empty string if response indicates success, otherwise set to the
+  // failure reason.
+  const std::string error_;
+};
+
+}  // namespace media_router
+
+#endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTE_RESPONSE_H_