NULL check web_contents_ to prevent a crash.

chrome/browser/jsmessage_box_handler_win.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/jsmessage_box_handler_win.h"
 
 #include "base/string_util.h"
 #include "chrome/browser/app_modal_dialog_queue.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/profile.h"
@@ skipping 66 matching lines @@
   if (dialog_flags_ & MessageBox::kFlagHasOKButton)
     dialog_buttons = DIALOGBUTTON_OK;
 
   if (dialog_flags_ & MessageBox::kFlagHasCancelButton)
     dialog_buttons |= DIALOGBUTTON_CANCEL;
 
   return dialog_buttons;
 }
 
 std::wstring JavascriptMessageBoxHandler::GetWindowTitle() const {
-  if (!frame_url_.has_host())
+  if (!frame_url_.has_host() || !web_contents_)
     return l10n_util::GetString(IDS_JAVASCRIPT_MESSAGEBOX_DEFAULT_TITLE);
 
   // We really only want the scheme, hostname, and port.
   GURL::Replacements replacements;
   replacements.ClearUsername();
   replacements.ClearPassword();
   replacements.ClearPath();
   replacements.ClearQuery();
   replacements.ClearRef();
   GURL clean_url = frame_url_.ReplaceComponents(replacements);
@@ skipping 84 matching lines @@
     return message_box_view_->text_box();
   return views::AppModalDialogDelegate::GetInitiallyFocusedView();
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 // JavascriptMessageBoxHandler, private:
 
 void JavascriptMessageBoxHandler::Observe(NotificationType type,
                                           const NotificationSource& source,
                                           const NotificationDetails& details) {
-  bool web_contents_gone = false;
   if (!web_contents_)
     return;
 
+  bool web_contents_gone = false;
+
   if (type == NotificationType::NAV_ENTRY_COMMITTED &&
       Source<NavigationController>(source).ptr() == web_contents_->controller())
     web_contents_gone = true;
 
   if (type == NotificationType::TAB_CONTENTS_DESTROYED &&
       Source<TabContents>(source).ptr() ==
       static_cast<TabContents*>(web_contents_))
     web_contents_gone = true;
 
   if (web_contents_gone) {
     web_contents_ = NULL;
 
     // If the dialog is visible close it.
     if (dialog_)
       dialog_->Close();
   }
 }