[Media Router] Force DEFAULT cast mode when starting presentations from content.

chrome/browser/ui/webui/media_router/media_router_ui.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_UI_WEBUI_MEDIA_ROUTER_MEDIA_ROUTER_UI_H_
 #define CHROME_BROWSER_UI_WEBUI_MEDIA_ROUTER_MEDIA_ROUTER_UI_H_
 
 #include <memory>
 #include <set>
 #include <string>
@@ skipping 134 matching lines @@
   const std::vector<MediaRoute>& routes() const { return routes_; }
   const std::vector<MediaRoute::Id>& joinable_route_ids() const {
     return joinable_route_ids_;
   }
   virtual const std::set<MediaCastMode>& cast_modes() const;
   const std::unordered_map<MediaRoute::Id, MediaCastMode>&
   routes_and_cast_modes() const {
     return routes_and_cast_modes_;
   }
   const content::WebContents* initiator() const { return initiator_; }
+  const base::Optional<MediaCastMode>& forced_cast_mode() const {
+    return forced_cast_mode_;
+  }
 
   virtual const std::string& GetRouteProviderExtensionId() const;
 
   // Called to track UI metrics.
   void SetUIInitializationTimer(const base::Time& start_time);
   void OnUIInitiallyLoaded();
   void OnUIInitialDataReceived();
 
   void UpdateMaxDialogHeight(int height);
 
@@ skipping 221 matching lines @@
   MediaRouter* router_;
 
   // The start time for UI initialization metrics timer. When a dialog has been
   // been painted and initialized with initial data, this should be cleared.
   base::Time start_time_;
 
   // The observer for the route controller. Notifies |handler_| of media status
   // updates.
   std::unique_ptr<UIMediaRouteControllerObserver> route_controller_observer_;
 
+  // If set, a cast mode that is required to be shown first.
+  base::Optional<MediaCastMode> forced_cast_mode_;
+
   // NOTE: Weak pointers must be invalidated before all other member variables.
   // Therefore |weak_factory_| must be placed at the end.
   base::WeakPtrFactory<MediaRouterUI> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaRouterUI);
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_UI_WEBUI_MEDIA_ROUTER_MEDIA_ROUTER_UI_H_