Add flag to enable immersive fullscreen for v2 apps

apps/ui/native_app_window.h

Index: apps/ui/native_app_window.h
diff --git a/apps/ui/native_app_window.h b/apps/ui/native_app_window.h
index 222a680512642d06e5165d4e3f3de210b877d596..a0ef5c9da60d08361c51396d2ce128ca15752be5 100644
--- a/apps/ui/native_app_window.h
+++ b/apps/ui/native_app_window.h
@@ -18,9 +18,11 @@ namespace apps {
 class NativeAppWindow : public ui::BaseWindow,
                         public web_modal::WebContentsModalDialogHost {
  public:
-  // Fullscreen changes may be asynchronous on some platforms.
-  virtual void SetFullscreen(bool fullscreen) = 0;
-  virtual bool IsFullscreenOrPending() const = 0;
+  // Sets whether the window is fullscreen and the type of fullscreen.
+  virtual void SetFullscreen(ShellWindow::FullscreenType type) = 0;
+
+  // Returns true if the window supports immersive fullscreen.
+  virtual bool SupportsImmersiveFullscreen() const = 0;
 
   // Returns true if the window is a panel that has been detached.
   virtual bool IsDetached() const = 0;