[Mac] Finish implementation of App Tabs.

chrome/browser/tabs/tab_strip_model.cc

 // Copyright (c) 2010 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/tabs/tab_strip_model.h"
 
 #include <algorithm>
 
 #include "base/command_line.h"
 #include "base/stl_util-inl.h"
@@ skipping 445 matching lines @@
 
 bool TabStripModel::IsTabPinned(int index) const {
   return contents_data_[index]->pinned;
 }
 
 bool TabStripModel::IsMiniTab(int index) const {
   return IsTabPinned(index) || IsAppTab(index);
 }
 
 bool TabStripModel::IsAppTab(int index) const {
-  return GetTabContentsAt(index)->is_app();
+  TabContents* contents = GetTabContentsAt(index);
+  return contents && contents->is_app();
 }
 
 bool TabStripModel::IsToolbarVisible(int index) const {
   Extension* extension_app = GetTabContentsAt(index)->extension_app();
   if (!extension_app)
     return true;
 
   ExtensionsService* service = profile()->GetExtensionsService();
   ExtensionPrefs* prefs = service->extension_prefs();
   return prefs->AreAppTabToolbarsVisible(extension_app->id());
@@ skipping 586 matching lines @@
   FOR_EACH_OBSERVER(TabStripModelObserver, observers_,
                     TabMoved(moved_data->contents, index, to_position));
 }
 
 // static
 bool TabStripModel::OpenerMatches(const TabContentsData* data,
                                   const NavigationController* opener,
                                   bool use_group) {
   return data->opener == opener || (use_group && data->group == opener);
 }