Make scroll-animations/css/ tests pass for run-snapshot-post-layout

Preparing for proposed change:

whatwg/html#11613

Bug: 384523570
Change-Id: I03bb632c6333c11dfe1081825dbea863a718c089
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6975917
Reviewed-by: Kevin Ellis <[email protected]>
Commit-Queue: Rune Lillesveen <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1523396}

Author: lilles

scroll-animations/css/scroll-timeline-multi-pass.tentative.html

@@ -105,6 +105,8 @@
       assert_equals(events2[0][0].contentBoxSize[0].blockSize, 1);
 
       assert_equals(getComputedStyle(element1).width, '100px');
+
+      await waitForNextFrame();
       assert_equals(getComputedStyle(element2).height, '100px');
     }, 'Multiple style/layout passes occur when necessary');
 </script>

scroll-animations/css/scroll-timeline-paused-animations.html

@@ -72,7 +72,7 @@
   await waitForNextFrame();
   const maxScroll = scroller.scrollHeight - scroller.clientHeight;
   scroller.scrollTop = maxScroll;
-  await waitForNextFrame();
+  await waitForCSSScrollTimelineStyle();
   assert_equals(getComputedStyle(div).width, '200px');
 
   div.style.animationPlayState = 'paused';
@@ -86,7 +86,7 @@
                 'Current time preserved when paused.');
   assert_percents_equal(anim.timeline.currentTime, 100);
   document.scrollingElement.scrollTop = 0;
-  await waitForNextFrame();
+  await waitForCSSScrollTimelineStyle();
   assert_percents_equal(anim.timeline.currentTime, 0);
   assert_equals(getComputedStyle(div).width, '200px');
 }, 'Test that the scroll animation is paused by updating animation-play-state');