WelcomeHandler sometimes has browser_ null in ctor

chrome/browser/ui/webui/welcome_handler.cc

Index: chrome/browser/ui/webui/welcome_handler.cc
diff --git a/chrome/browser/ui/webui/welcome_handler.cc b/chrome/browser/ui/webui/welcome_handler.cc
index f23d092abea7153cdd0a8f17eaad2eb1b8817692..b06ea2bd3d9e8ddabc356fdf3ce930e56904d5d7 100644
--- a/chrome/browser/ui/webui/welcome_handler.cc
+++ b/chrome/browser/ui/webui/welcome_handler.cc
@@ -46,6 +46,11 @@ void WelcomeHandler::HandleActivateSignIn(const base::ListValue* args) {
     // 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);