javascript build fix

platform/javascript/os_javascript.cpp

@@ -230,6 +230,12 @@ OS::VideoMode OS_JavaScript::get_video_mode(int p_screen) const {
 
 	return default_videomode;
 }
+
+Size2 OS_JavaScript::get_screen_size(int p_screen) const {
+
+	return Vector2(default_videomode.width,default_videomode.height);
+}
+
 void OS_JavaScript::get_fullscreen_mode_list(List<VideoMode> *p_list,int p_screen) const {
 
 	p_list->push_back(default_videomode);

platform/javascript/os_javascript.h

@@ -127,6 +127,7 @@ public:
 	virtual VideoMode get_video_mode(int p_screen=0) const;
 	virtual void get_fullscreen_mode_list(List<VideoMode> *p_list,int p_screen=0) const;
 
+	virtual Size2 get_screen_size(int p_screen=0) const;
 	virtual String get_name();
 	virtual MainLoop *get_main_loop() const;