Allow unloading a movie by sending `None` to `replace_with_movie`.

This also adjusts `MovieClip.unloadMovie` to do just that, instead of removing the clip from the display list. We also have to unload clips when loading new movies into them, since `unloadMovie` desugars to loading `""` as the URL.

core/src/avm1/globals/movie_clip.rs

@@ -228,29 +228,8 @@ pub fn create_proto<'gc>(
             Ok(Value::Undefined.into())
         },
         "unloadMovie" => |mut target: MovieClip<'gc>, _avm: &mut Avm1<'gc>, context: &mut UpdateContext<'_, 'gc, '_>, _args: &[Value<'gc>]| {
-            //TODO: How do we reclaim resources from unloaded movies?
-            if let Some(parent) = target.parent() {
-                parent
-                    .as_movie_clip()
-                    .unwrap()
-                    .remove_child_from_avm(context, DisplayObject::MovieClip(target));
-            } else {
-                //Removing a layer is a little different.
-                let mut layer_depth = None;
-
-                for (depth, layer) in context.layers.iter() {
-                    if DisplayObject::ptr_eq(*layer, DisplayObject::MovieClip(target)) {
-                        layer_depth = Some(*depth);
-                        break;
-                    }
-                }
-
-                if let Some(depth) = layer_depth {
-                    context.layers.remove(&depth);
-                }
-
-                target.unload(context);
-            }
+            target.unload(context);
+            target.replace_with_movie(context.gc_context, None);
 
             Ok(Value::Undefined.into())
         }

core/src/display_object/movie_clip.rs

@@ -111,7 +111,7 @@ impl<'gc> MovieClip<'gc> {
     pub fn replace_with_movie(
         &mut self,
         gc_context: MutationContext<'gc, '_>,
-        movie: Arc<SwfMovie>,
+        movie: Option<Arc<SwfMovie>>,
     ) {
         self.0
             .write(gc_context)
@@ -424,13 +424,17 @@ impl<'gc> MovieClipData<'gc> {
     /// Replace the current MovieClipData with a completely new SwfMovie.
     ///
     /// Playback will start at position zero, any existing streamed audio will
-    /// be terminated, and so on. Children and AVM data will be kept across the
-    /// load boundary.
+    /// be terminated, and so on. Children and AVM data will NOT be kept across
+    /// the load boundary.
+    ///
+    /// If no movie is provided, then the movie clip will be replaced with an
+    /// empty movie of the same SWF version.
     pub fn replace_with_movie(
         &mut self,
         gc_context: MutationContext<'gc, '_>,
-        movie: Arc<SwfMovie>,
+        movie: Option<Arc<SwfMovie>>,
     ) {
+        let movie = movie.unwrap_or_else(|| Arc::new(SwfMovie::empty(self.movie().version())));
         let total_frames = movie.header().num_frames;
 
         self.base = Default::default();

core/src/loader.rs

@@ -211,6 +211,12 @@ impl<'gc> Loader<'gc> {
                         _ => unreachable!(),
                     };
 
+                    clip.as_movie_clip().unwrap().unload(uc);
+
+                    clip.as_movie_clip()
+                        .unwrap()
+                        .replace_with_movie(uc.gc_context, None);
+
                     if let Some(broadcaster) = broadcaster {
                         avm.insert_stack_frame_for_method(
                             clip,
@@ -264,7 +270,7 @@ impl<'gc> Loader<'gc> {
                             .as_movie_clip()
                             .expect("Attempted to load movie into not movie clip");
 
-                        mc.replace_with_movie(uc.gc_context, movie.clone());
+                        mc.replace_with_movie(uc.gc_context, Some(movie.clone()));
                         mc.post_instantiation(uc.gc_context, clip, avm.prototypes().movie_clip);
 
                         let mut morph_shapes = fnv::FnvHashMap::default();