Allow MediaRouterDialogControllerImpl to re-set its reference to MRAction

chrome/browser/ui/webui/media_router/media_router_dialog_controller_impl.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_DIALOG_CONTROLLER_IMPL_H_
 #define CHROME_BROWSER_UI_WEBUI_MEDIA_ROUTER_MEDIA_ROUTER_DIALOG_CONTROLLER_IMPL_H_
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
@@ skipping 15 matching lines @@
  public:
   ~MediaRouterDialogControllerImpl() override;
 
   static MediaRouterDialogControllerImpl* GetOrCreateForWebContents(
       content::WebContents* web_contents);
 
   // Returns the media router dialog WebContents.
   // Returns nullptr if there is no dialog.
   content::WebContents* GetMediaRouterDialog() const;
 
-  // |action| must always be non-null.
+  // Sets the action to notify when a dialog gets shown or hidden.
   void SetMediaRouterAction(const base::WeakPtr<MediaRouterAction>& action);
 
   // MediaRouterDialogController:
   bool IsShowingMediaRouterDialog() const override;
 
   void UpdateMaxDialogSize();
 
  private:
   class DialogWebContentsObserver;
   friend class content::WebContentsUserData<MediaRouterDialogControllerImpl>;
@@ skipping 29 matching lines @@
   base::WeakPtr<MediaRouterAction> action_;
 
   base::WeakPtrFactory<MediaRouterDialogControllerImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaRouterDialogControllerImpl);
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_UI_WEBUI_MEDIA_ROUTER_MEDIA_ROUTER_DIALOG_CONTROLLER_IMPL_H_