Create BrowserUserData.

ios/shared/chrome/browser/ui/browser_list/browser.h

 // Copyright 2017 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 IOS_SHARED_CHROME_BROWSER_UI_BROWSER_LIST_BROWSER_H_
 #define IOS_SHARED_CHROME_BROWSER_UI_BROWSER_LIST_BROWSER_H_
 
 #include <memory>
 
 #include "base/macros.h"
+#include "base/supports_user_data.h"
 
 class WebStateList;
 class WebStateListDelegate;
 
 @class ChromeBroadcaster;
 @class CommandDispatcher;
 
 namespace ios {
 class ChromeBrowserState;
 }
 
 // Browser holds the state backing a collection of Tabs and the attached
 // UI elements (Tab strip, ...).
-class Browser {
+class Browser : public base::SupportsUserData {
  public:
   explicit Browser(ios::ChromeBrowserState* browser_state);
-  ~Browser();
+  ~Browser() override;
 
   WebStateList& web_state_list() { return *web_state_list_.get(); }
   const WebStateList& web_state_list() const { return *web_state_list_.get(); }
 
   CommandDispatcher* dispatcher() { return dispatcher_; }
 
   ios::ChromeBrowserState* browser_state() const { return browser_state_; }
 
   ChromeBroadcaster* broadcaster() { return broadcaster_; }
 
  private:
   __strong ChromeBroadcaster* broadcaster_;
   __strong CommandDispatcher* dispatcher_;
   ios::ChromeBrowserState* browser_state_;
   std::unique_ptr<WebStateListDelegate> web_state_list_delegate_;
   std::unique_ptr<WebStateList> web_state_list_;
 
   DISALLOW_COPY_AND_ASSIGN(Browser);
 };
 
 #endif  // IOS_SHARED_CHROME_BROWSER_UI_BROWSER_LIST_BROWSER_H_