Removes _isContainer

src/flash/display/SimpleButton.js

@@ -27,9 +27,6 @@ const SimpleButtonDefinition = (function () {
       this._upState = val;
     },
 
-    get _isContainer() {
-      return true;
-    },
     _getAS2Object: function () {
       if (!this.$as2Object) {
         new AS2Button().$attachNativeObject(this);

src/swf/renderer.js

@@ -2,6 +2,7 @@ function renderStage(stage, ctx) {
   // All the visitors close over this class to do instance testing.
   const MovieClipClass = avm2.systemDomain.getClass("flash.display.MovieClip");
   const ContainerClass = avm2.systemDomain.getClass("flash.display.DisplayObjectContainer");
+  const SimpleButtonClass = avm2.systemDomain.getClass("flash.display.SimpleButton");
   const InteractiveClass = avm2.systemDomain.getClass("flash.display.InteractiveObject");
 
   function visitContainer(container, visitor, interactiveParent) {
@@ -10,7 +11,8 @@ function renderStage(stage, ctx) {
     for (var i = 0, n = children.length; i < n; i++) {
       var child = children[i];
       if (child) {
-        var isContainer = ContainerClass.isInstanceOf(child) || child._isContainer;
+        var isContainer = ContainerClass.isInstanceOf(child) ||
+                          SimpleButtonClass.isInstanceOf(child);
 
         if (InteractiveClass.isInstanceOf(child)) {
           if (!interactiveParent || interactiveParent._mouseChildren)