Null checks to prevent occasional crash

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 133 matching lines @@
                         on_close_success,
                         profile->GetPath());
 }
 
 // static
 void BrowserList::TryToCloseBrowserList(const BrowserVector& browsers_to_close,
     const base::Callback<void(const base::FilePath&)>& on_close_success,
     const base::FilePath& profile_path) {
   for (BrowserVector::const_iterator it = browsers_to_close.begin();
        it != browsers_to_close.end(); ++it) {
+    // TODO(mlerman): crbug.com/423229, if we can determine why window() is
+    // false we can better solve the underlying issue here.
+    CHECK((*it)->window());
     if ((*it)->CallBeforeUnloadHandlers(
             base::Bind(&BrowserList::PostBeforeUnloadHandlers,
                        browsers_to_close,
                        on_close_success,
                        profile_path))) {
       return;
     }
   }
 
   on_close_success.Run(profile_path);
 
   for (BrowserVector::const_iterator it = browsers_to_close.begin();
-       it != browsers_to_close.end(); ++it)
+       it != browsers_to_close.end(); ++it) {
+    // TODO(mlerman): If reproducible, determine cause if window() being null.
+    CHECK((*it));
+    CHECK((*it)->window());
     (*it)->window()->Close();
+  }
 }
 
 // static
 void BrowserList::PostBeforeUnloadHandlers(
     const BrowserVector& browsers_to_close,
     const base::Callback<void(const base::FilePath&)>& on_close_success,
     const base::FilePath& profile_path,
     bool tab_close_confirmed) {
   // We need this bool to avoid infinite recursion when resetting the
   // BeforeUnload handlers, since doing that will trigger calls back to this
@@ skipping 55 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);
 }