Add the ability to load multiple apps into app_shell.

extensions/shell/browser/desktop_controller.h

Index: extensions/shell/browser/desktop_controller.h
diff --git a/extensions/shell/browser/desktop_controller.h b/extensions/shell/browser/desktop_controller.h
index 116d692a6cb6b35f9e4674576d17f685b9f1d505..40a4e537e8ab2f0395953d6de56a7be27ff89719 100644
--- a/extensions/shell/browser/desktop_controller.h
+++ b/extensions/shell/browser/desktop_controller.h
@@ -46,6 +46,9 @@ class DesktopController {
   // Attaches the window to our window hierarchy.
   virtual void AddAppWindow(aura::Window* window) = 0;
 
+  // Removes the window from the desktop.
+  virtual void RemoveAppWindow(AppWindow* window) = 0;
+
   // Closes and destroys the app windows.
   virtual void CloseAppWindows() = 0;
 };