fixed iphone build with new window manamenet changes

platform/iphone/os_iphone.cpp

@@ -474,6 +474,11 @@ String OSIPhone::get_name() {
 	return "iOS";
 };
 
+Size2 OSIPhone::get_window_size() const {
+	
+	return Vector2(video_mode.width, video_mode.height);
+}
+
 bool OSIPhone::has_touchscreen_ui_hint() const {
 
 	return true;

platform/iphone/os_iphone.h

@@ -167,6 +167,8 @@ public:
 	virtual void hide_virtual_keyboard();
 
 	virtual void set_cursor_shape(CursorShape p_shape);
+	
+	virtual Size2 get_window_size() const;
 
 	virtual bool has_touchscreen_ui_hint() const;