Fix crasher when closing tab with bad SSL constrained popup

chrome/browser/ssl_blocking_page.cc

 // Copyright (c) 2006-2008 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/ssl_blocking_page.h"
 
 #include "base/string_piece.h"
 #include "chrome/browser/browser.h"
 #include "chrome/browser/browser_resources.h"
 #include "chrome/browser/cert_store.h"
@@ skipping 153 matching lines @@
                               const NotificationSource& source,
                               const NotificationDetails& details) {
   switch (type) {
     case NOTIFY_TAB_CLOSING:
     case NOTIFY_INTERSTITIAL_PAGE_CLOSED: {
       // We created a navigation entry for the interstitial, remove it.
       // Note that we don't remove the entry if we are closing all tabs so that
       // the last entry is kept for the restoring on next start-up.
       Browser* browser = Browser::GetBrowserForController(tab_->controller(),
                                                           NULL);
-      if (remove_last_entry_ &&
+      // We may not have a browser (this is the case for constrained popups), in
+      // which case it does not matter if we do not remove the temporary entry
+      // as their navigation history is not saved.
+      if (remove_last_entry_ && browser &&
           !browser->tabstrip_model()->closing_all()) {
         tab_->controller()->RemoveLastEntry();
       }
       delete this;
       break;
     }
     case NOTIFY_DOM_OPERATION_RESPONSE: {
       std::string json =
           Details<DomOperationNotificationDetails>(details)->json();
       if (json == "1") {
@@ skipping 98 matching lines @@
   };
   int i;
   for (i = 0; i < static_cast<int>(extra_info.size()); i++) {
     strings->SetString(keys[i], extra_info[i]);
   }
   for (;i < 5; i++) {
     strings->SetString(keys[i], L"");
   }
 }