fixed build error on OSX from new WM code

platform/osx/os_osx.h

@@ -133,6 +133,8 @@ public:
 	virtual Point2 get_mouse_pos() const;
 	virtual int get_mouse_button_state() const;
 	virtual void set_window_title(const String& p_title);
+	
+	virtual Size2 get_window_size() const;
 
 	virtual void set_icon(const Image& p_icon);
 

platform/osx/os_osx.mm

@@ -1245,6 +1245,10 @@ void OS_OSX::get_fullscreen_mode_list(List<VideoMode> *p_list,int p_screen) cons
 
 }
 
+Size2 OS_OSX::get_window_size() const {
+	return Vector2(current_videomode.width, current_videomode.height);
+}
+
 void OS_OSX::move_window_to_foreground() {
 
 	[window_object orderFrontRegardless];