Fix TryToCloseBrowserList not checking for null callbacks

chrome/browser/ui/browser_list.cc

 // Copyright (c) 2012 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/browser_list.h"
 
 #include <algorithm>
 
 #include "base/auto_reset.h"
 #include "base/logging.h"
@@ skipping 147 matching lines @@
        it != browsers_to_close.end(); ++it) {
     if ((*it)->TryToCloseWindow(
             skip_beforeunload,
             base::Bind(&BrowserList::PostTryToCloseBrowserWindow,
                        browsers_to_close, on_close_success, on_close_aborted,
                        profile_path, skip_beforeunload))) {
       return;
     }
   }
 
-  on_close_success.Run(profile_path);
+  if (on_close_success)
+    on_close_success.Run(profile_path);
 
   for (Browser* b : browsers_to_close) {
     // BeforeUnload handlers may close browser windows, so we need to explicitly
     // check whether they still exist.
     if (b->window())
       b->window()->Close();
   }
 }
 
 // static
@@ skipping 11 matching lines @@
 
   if (tab_close_confirmed) {
     TryToCloseBrowserList(browsers_to_close, on_close_success, on_close_aborted,
                           profile_path, skip_beforeunload);
   } else if (!resetting_handlers) {
     base::AutoReset<bool> resetting_handlers_scoper(&resetting_handlers, true);
     for (BrowserVector::const_iterator it = browsers_to_close.begin();
          it != browsers_to_close.end(); ++it) {
       (*it)->ResetTryToCloseWindow();
     }
-    on_close_aborted.Run(profile_path);
+    if (on_close_aborted)
+      on_close_aborted.Run(profile_path);
   }
 }
 
 // static
 void BrowserList::MoveBrowsersInWorkspaceToFront(
     const std::string& new_workspace) {
   DCHECK(!new_workspace.empty());
 
   BrowserList* instance = GetInstance();
 
@@ skipping 74 matching lines @@
 }
 
 // static
 void BrowserList::RemoveBrowserFrom(Browser* browser,
                                     BrowserVector* browser_list) {
   BrowserVector::iterator remove_browser =
       std::find(browser_list->begin(), browser_list->end(), browser);
   if (remove_browser != browser_list->end())
     browser_list->erase(remove_browser);
 }