Use TreeCountingChecker in scale interpolations

Invalidate scale interpolation for tree counting function changes
on DOM mutations.

Also change TreeCountingChecker to take a CSSLengthResolver instead of
a StyleResolverState.

Bug: 415626999
Change-Id: I7a9ca34f87a6ce3b36df3cf30eb40c4637ae19aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6534157
Reviewed-by: Anders Hartvoll Ruud 
Commit-Queue: Rune Lillesveen 
Cr-Commit-Position: refs/heads/main@{#1459320}

Author: lilles

css/css-values/tree-counting/sibling-index-keyframe-scale-dynamic.html

@@ -0,0 +1,34 @@
+>
+<title>CSS Values and Units Test: sibling-index() changing scale() during @keyframes animationtitle>
+<link rel="help" href="https://drafts.csswg.org/css-values-5/#tree-counting">
+<script src="/resources/testharness.js">script>
+<script src="/resources/testharnessreport.js">script>
+<style>
+  @keyframes --anim {
+    from {
+      scale: 0.7 calc(0.2 * sibling-index());
+    }
+    to {
+      scale: 0.3 2;
+    }
+  }
+  #target {
+    animation: --anim 1000s step-end;
+  }
+style>
+<div>
+  <div id="rm">div>
+  <div>div>
+  <div id="target">div>
+div>
+<script>
+  test(() => {
+    assert_equals(getComputedStyle(target).scale, "0.7 0.6");
+  }, "Initially, the sibling-index() is 3 for #target");
+
+  test(() => {
+    rm.remove();
+    assert_equals(getComputedStyle(target).scale, "0.7 0.4");
+  }, "Removing a preceding sibling of #target reduces the sibling-index()");
+
+script>