Views - init less stuff in tabless browsers.

chrome/browser/ui/views/toolbar/toolbar_view.h

 // Copyright 2013 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.
 
 #ifndef CHROME_BROWSER_UI_VIEWS_TOOLBAR_TOOLBAR_VIEW_H_
 #define CHROME_BROWSER_UI_VIEWS_TOOLBAR_TOOLBAR_VIEW_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
@@ skipping 184 matching lines @@
   void ShowCriticalNotification();
 
   // Shows the outdated install notification bubble against the app menu.
   // |auto_update_enabled| is set to true when auto-upate is on.
   void ShowOutdatedInstallNotification(bool auto_update_enabled);
 
   void OnShowHomeButtonChanged();
 
   int content_shadow_height() const;
 
-  // Controls
+  // Controls. Most of these can be null, e.g. in popup windows. Only
+  // |location_bar_| is guaranteed to exist.
   BackButton* back_;
   ToolbarButton* forward_;
   ReloadButton* reload_;
   HomeButton* home_;
   LocationBarView* location_bar_;
   BrowserActionsContainer* browser_actions_;
   AppMenuButton* app_menu_button_;
+
   Browser* browser_;
 
   AppMenuBadgeController badge_controller_;
 
   // Controls whether or not a home button should be shown on the toolbar.
   BooleanPrefMember show_home_button_;
 
   // The display mode used when laying out the toolbar.
-  DisplayMode display_mode_;
+  const DisplayMode display_mode_;
 
   content::NotificationRegistrar registrar_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(ToolbarView);
 };
 
 #endif  // CHROME_BROWSER_UI_VIEWS_TOOLBAR_TOOLBAR_VIEW_H_