avm2: Move child construction work to Sprite constructor

This change should not be observable, as no other `DisplayObject` subclasses can have timeline children

Author: Lord-McSweeney

core/src/avm2/globals/flash/display/DisplayObject.as

@@ -17,8 +17,6 @@ package flash.display {
     public class DisplayObject extends EventDispatcher implements IBitmapDrawable {
         private var _accessibilityProperties:AccessibilityProperties;
 
-        public native function DisplayObject();
-
         public function get accessibilityProperties():AccessibilityProperties {
             return this._accessibilityProperties;
         }

core/src/avm2/globals/flash/display/Sprite.as

@@ -6,10 +6,16 @@ package flash.display {
 
     [Ruffle(InstanceAllocator)]
     public class Sprite extends DisplayObjectContainer {
-
         [Ruffle(NativeAccessible)]
         private var _graphics:Graphics;
 
+        public function Sprite() {
+            super();
+            this.constructChildren();
+        }
+
+        private native function constructChildren():void;
+
         public native function get graphics():Graphics;
         public native function get dropTarget():DisplayObject;
         public native function get soundTransform():SoundTransform;

core/src/avm2/globals/flash/display/display_object.rs

@@ -53,35 +53,6 @@ pub fn initialize_for_allocator<'gc>(
     obj.into()
 }
 
-/// Implements `flash.display.DisplayObject`'s native instance constructor.
-pub fn display_object_initializer<'gc>(
-    activation: &mut Activation<'_, 'gc>,
-    this: Value<'gc>,
-    _args: &[Value<'gc>],
-) -> Result<Value<'gc>, Error<'gc>> {
-    // No need to call `super()`, it wouldn't do anything
-
-    let this = this.as_object().unwrap();
-
-    if let Some(dobj) = this.as_display_object() {
-        if let Some(clip) = dobj.as_movie_clip() {
-            clip.set_constructing_frame(true);
-        }
-
-        if let Some(container) = dobj.as_container() {
-            for child in container.iter_render_list() {
-                child.construct_frame(activation.context);
-            }
-        }
-
-        if let Some(clip) = dobj.as_movie_clip() {
-            clip.set_constructing_frame(false);
-        }
-    }
-
-    Ok(Value::Undefined)
-}
-
 /// Implements `alpha`'s getter.
 pub fn get_alpha<'gc>(
     _activation: &mut Activation<'_, 'gc>,

core/src/avm2/globals/flash/display/sprite.rs

@@ -9,7 +9,7 @@ use crate::avm2::globals::slots::{
 use crate::avm2::object::{ClassObject, Object, StageObject, TObject as _};
 use crate::avm2::parameters::ParametersExt;
 use crate::avm2::value::Value;
-use crate::display_object::{MovieClip, SoundTransform, TDisplayObject};
+use crate::display_object::{MovieClip, SoundTransform, TDisplayObject, TDisplayObjectContainer};
 use swf::{Rectangle, Twips};
 
 pub fn sprite_allocator<'gc>(
@@ -58,6 +58,25 @@ pub fn sprite_allocator<'gc>(
     unreachable!("A Sprite subclass should have Sprite in superclass chain");
 }
 
+pub fn construct_children<'gc>(
+    activation: &mut Activation<'_, 'gc>,
+    this: Value<'gc>,
+    _args: &[Value<'gc>],
+) -> Result<Value<'gc>, Error<'gc>> {
+    let this = this.as_object().unwrap();
+    let this = this.as_display_object().unwrap();
+    let clip = this.as_movie_clip().unwrap();
+
+    // Construct children of this Sprite
+    clip.set_constructing_frame(true);
+    for child in clip.iter_render_list() {
+        child.construct_frame(activation.context);
+    }
+    clip.set_constructing_frame(false);
+
+    Ok(Value::Undefined)
+}
+
 /// Implements `dropTarget`'s getter
 pub fn get_drop_target<'gc>(
     _activation: &mut Activation<'_, 'gc>,

core/src/display_object/movie_clip.rs

@@ -2475,7 +2475,7 @@ impl<'gc> TDisplayObject<'gc> for MovieClip<'gc> {
                 self.construct_as_avm2_object(context);
                 self.on_construction_complete(context);
                 // If we're in the load frame and we were constructed by ActionScript,
-                // then we want to wait for the DisplayObject constructor to run
+                // then we want to wait for the Sprite constructor to run
                 // 'construct_frame' on children. This is observable by ActionScript -
                 // before calling super(), 'this.numChildren' will show a non-zero number
                 // when we have children placed on the load frame, but 'this.getChildAt(0)'