Add a specialized apps::NativeAppWindow for app_shell

apps/shell/browser/shell_extension_system.cc

Index: apps/shell/browser/shell_extension_system.cc
diff --git a/apps/shell/browser/shell_extension_system.cc b/apps/shell/browser/shell_extension_system.cc
index 324368fa76c7681a133da40b0223391447accf41..e47602b43304a86aa02a9e16a5eb76df1b5dc9e2 100644
--- a/apps/shell/browser/shell_extension_system.cc
+++ b/apps/shell/browser/shell_extension_system.cc
@@ -6,6 +6,7 @@
 
 #include <string>
 
+#include "apps/shell_window_registry.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "chrome/browser/chrome_notification_types.h"
@@ -59,6 +60,7 @@ bool ShellExtensionSystem::LoadAndLaunchApp(const base::FilePath& app_dir) {
         << " failed with: " << load_error;
     return false;
   }
+  app_id_ = extension->id();
 
   // TODO(jamescook): We may want to do some of these things here:
   // * Create a PermissionsUpdater.
@@ -97,6 +99,11 @@ bool ShellExtensionSystem::LoadAndLaunchApp(const base::FilePath& app_dir) {
   return true;
 }
 
+void ShellExtensionSystem::CloseApp() {
+  apps::ShellWindowRegistry::Get(browser_context_)
+      ->CloseAllShellWindowsForApp(app_id_);
+}
+
 void ShellExtensionSystem::Shutdown() {
 }