Links in platform apps should open in the system default browser.

chrome/browser/ui/extensions/shell_window.h

 // 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.
 
 #ifndef CHROME_BROWSER_UI_EXTENSIONS_SHELL_WINDOW_H_
 #define CHROME_BROWSER_UI_EXTENSIONS_SHELL_WINDOW_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/extensions/extension_function_dispatcher.h"
 #include "chrome/browser/sessions/session_id.h"
 #include "chrome/browser/ui/base_window.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/web_contents_delegate.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/common/console_message_level.h"
 #include "ui/gfx/rect.h"
 
 class GURL;
 class Profile;
 class TabContents;
 class NativeShellWindow;
+class ExternalWebContentImpl;
 
 namespace content {
 class WebContents;
 }
 
 namespace extensions {
 class Extension;
 class PlatformAppBrowserTest;
 class WindowController;
 
@@ skipping 135 matching lines @@
   // window.
   std::string window_key_;
 
   const SessionID session_id_;
   scoped_ptr<TabContents> contents_;
   // web_contents_ is owned by contents_.
   content::WebContents* web_contents_;
   content::NotificationRegistrar registrar_;
   ExtensionFunctionDispatcher extension_function_dispatcher_;
 
+  // Web content delegate for link navigation.
+  scoped_ptr<ExternalWebContentImpl> external_content_delegate_;
+
   scoped_ptr<NativeShellWindow> native_window_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellWindow);
 };
 
 #endif  // CHROME_BROWSER_UI_EXTENSIONS_SHELL_WINDOW_H_