WelcomeHandler sometimes has browser_ null in ctor

chrome/browser/ui/webui/welcome_handler.cc

 // 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.
 
 #include "chrome/browser/ui/webui/welcome_handler.h"
 
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/signin/profile_oauth2_token_service_factory.h"
 #include "chrome/browser/signin/signin_manager_factory.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/ui/browser_navigator.h"
 #include "chrome/browser/ui/profile_chooser_constants.h"
 #include "chrome/common/url_constants.h"
 #include "components/signin/core/browser/signin_manager.h"
 #include "components/signin/core/browser/signin_metrics.h"
 #include "ui/base/page_transition_types.h"
 
 WelcomeHandler::WelcomeHandler(content::WebUI* web_ui)
     : profile_(Profile::FromWebUI(web_ui)),
       browser_(chrome::FindBrowserWithWebContents(web_ui->GetWebContents())),

[Dan Beam, 2016/10/18 21:01:54]

can we just make a

Browser* WelcomeHandler::GetBrowser() {
  DCHECK(web_ui());
  content::WebContents* contents = web_ui()->GetWebContents();
  DCHECK(contents);
  Browser* browser = chrome::FindBrowserWithWebContents(contents);
  DCHECK(browser);
  return browser;
}

and use it everywhere instead of browser_?

       oauth2_token_service_(
           ProfileOAuth2TokenServiceFactory::GetForProfile(profile_)),
       result_(WelcomeResult::DEFAULT) {
   oauth2_token_service_->AddObserver(this);
 }
 
 WelcomeHandler::~WelcomeHandler() {
   oauth2_token_service_->RemoveObserver(this);
   // TODO(tmartino): Log to UMA according to WelcomeResult.
 }
 
 // Override from OAuth2TokenService::Observer. Occurs when a new auth token is
 // available.
 void WelcomeHandler::OnRefreshTokenAvailable(const std::string& account_id) {
   result_ = WelcomeResult::SIGNED_IN;
   GoToNewTabPage();
 }
 
 // Handles backend events necessary when user clicks "Sign in."
 void WelcomeHandler::HandleActivateSignIn(const base::ListValue* args) {
   if (SigninManagerFactory::GetForProfile(profile_)->IsAuthenticated()) {
     // In general, this page isn't shown to signed-in users; however, if one
     // should arrive here, then opening the sign-in dialog will likely lead
     // to a crash. Thus, we just act like sign-in was "successful" and whisk
     // them away to the NTP instead.
     GoToNewTabPage();
   } else {
+    // browser_ does not always properly initialize in the constructor.
+    // https://crbug.com/656153

[dpapad, 2016/10/18 18:17:02]

+dbeam who might know more about WebUI lifetime related issues.

@dbeam: Do you know if this a known issue? Does it happen on other WebUI pages?

+    if (browser_ == nullptr) {
+      browser_ = chrome::FindBrowserWithWebContents(web_ui()->GetWebContents());
+    }
     browser_->ShowModalSigninWindow(
         profiles::BubbleViewMode::BUBBLE_VIEW_MODE_GAIA_SIGNIN,
         signin_metrics::AccessPoint::ACCESS_POINT_START_PAGE);
   }
 }
 
 // Handles backend events necessary when user clicks "No thanks."
 void WelcomeHandler::HandleUserDecline(const base::ListValue* args) {
   result_ = WelcomeResult::DECLINED;
   GoToNewTabPage();
 }
 
 // Override from WebUIMessageHandler.
 void WelcomeHandler::RegisterMessages() {
   web_ui()->RegisterMessageCallback(
       "handleActivateSignIn", base::Bind(&WelcomeHandler::HandleActivateSignIn,
                                          base::Unretained(this)));
   web_ui()->RegisterMessageCallback(
       "handleUserDecline",
       base::Bind(&WelcomeHandler::HandleUserDecline, base::Unretained(this)));
 }
 
 void WelcomeHandler::GoToNewTabPage() {
   chrome::NavigateParams params(browser_, GURL(chrome::kChromeUINewTabURL),
                                 ui::PageTransition::PAGE_TRANSITION_LINK);
   chrome::Navigate(&params);
 }