tests: Add focus_highlight_empty_clip test

tests/tests/swfs/visual/focus_highlight/focus_highlight_empty_clip/Test.as

@@ -0,0 +1,31 @@
+package {
+
+import flash.display.MovieClip;
+import flash.display.Sprite;
+
+[SWF(width="50", height="50", backgroundColor="#000000")]
+public class Test extends MovieClip {
+    public function Test() {
+        super();
+
+        var sprite:Sprite = new Sprite();
+        sprite.graphics.beginFill(0xFF00FF);
+        sprite.graphics.drawRect(0, 0, 20, 20);
+
+        // 1. Create a movie clip and add it as a child.
+        var clip:MovieClip = new MovieClip();
+        var clip2:MovieClip = new MovieClip();
+        addChild(clip);
+        clip.addChild(clip2);
+
+        clip.x = 15;
+        clip.y = 15;
+
+        // 2. Focus the empty clip.
+        stage.focus = clip;
+
+        // 3. Add some content to the clip after being focused.
+        clip2.addChild(sprite);
+    }
+}
+}

tests/tests/swfs/visual/focus_highlight/focus_highlight_empty_clip/test.toml

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+num_ticks = 1
+
+image_comparisons."output".trigger = 1
+
+[player_options]
+with_renderer = { optional = false, sample_count = 1 }