Switch to animating visibility, remove flicker

ts/sequence_tile.ts

@@ -19,23 +19,23 @@ export class SequenceTile extends AnimatableTile {
       tile.elem.style.position = 'absolute';
       tile.elem.style.top = '0';
       tile.elem.style.left = '0';
-      tile.elem.style.opacity = '0.0';
+      tile.elem.style.visibility = 'hidden';
 
       animation = tile.elem.animate(
         [
           {
             'offset': 0,
             'easing': 'step-end',
-            'opacity': '0.0',
+            'visibility': 'hidden',
           },
           {
             'offset': i * tile_chunk,
             'easing': 'step-end',
-            'opacity': '1.0',
+            'visibility': 'visible',
           },
           {
             'offset': (i + 1) * tile_chunk,
-            'opacity': '0.0',
+            'visibility': 'hidden',
           },
         ],
         {