WelcomeHandler sometimes has browser_ null in ctor

chrome/browser/ui/webui/welcome_handler.h

 // Copyright 2016 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_WELCOME_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_WELCOME_HANDLER_H_
 
 #include "base/macros.h"
 #include "content/public/browser/web_ui_message_handler.h"
 #include "google_apis/gaia/oauth2_token_service.h"
@@ skipping 19 matching lines @@
   enum WelcomeResult {
     DEFAULT = 0,
     SIGNED_IN,  // User clicked the "Sign In" button and completed sign-in.
     DECLINED    // User clicked the "No Thanks" button.
   };
 
   void HandleActivateSignIn(const base::ListValue* args);
   void HandleUserDecline(const base::ListValue* args);
   void GoToNewTabPage();
 
+  Browser* GetBrowser();
+
   Profile* profile_;
-  Browser* browser_;
   ProfileOAuth2TokenService* oauth2_token_service_;
   WelcomeResult result_;
 
   DISALLOW_COPY_AND_ASSIGN(WelcomeHandler);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_WELCOME_HANDLER_H_