Fix <meta> post-insertion steps expectations

See whatwg/html#10241 for the recommendation
to change these test expectations to align with Chromium and WebKit's
behavior.

FWIW, I did try and change the processing of these kinds of meta tags
in Chromium to use the insertion steps [1], and without any extra work
at least, this caused a bunch of crashes [2].

So this change (changing the test expectations) is easier, and aligns
with more browsers.

[1]: https://crrev.com/c/5399060
[2]: https://crbug.com/330694762

[email protected]

Bug: 40150299, 330694762
Change-Id: I60f8ba556984bc1e8df4ba6e1dc375b1dfb7823d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5410497
Reviewed-by: Noam Rosenthal <[email protected]>
Commit-Queue: Dominic Farolino <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1281241}

dom/nodes/insertion-removing-steps/Node-appendChild-script-and-default-style-meta-from-fragment.tentative.html

@@ -7,29 +7,53 @@
 <div id="div">hello</div>
 <script>
 let scriptRan = false;
-let computedStyleDuringInsertion = null;
+let computedStyleInPreScript = null;
+let computedStyleInPostScript = null;
 test(() => {
   const div = document.getElementById("div");
+
+  // 1. Gets inserted *before* the `<meta>` tag. Cannot observe the meta tag's
+  // effect, because this script runs before the meta tag's post-insertion steps
+  // run, and the meta tag's post-insertion steps is where the default style
+  // sheet actually changes.
+  const preScript = document.createElement("script");
+  preScript.textContent =  `
+    computedStyleInPreScript = getComputedStyle(div).display;
+    scriptRan = true;
+  `;
+
+  // 2. The `<meta>` tag itself.
   const meta = document.createElement("meta");
   meta.httpEquiv = "default-style";
   meta.content = "alternative";
-  const script = document.createElement("script");
-  script.textContent = `
-    computedStyleDuringInsertion = getComputedStyle(div).display;
+
+  // 3. Gets inserted *after* the `<meta>` tag. Observes the meta tag's effect,
+  // because this script runs after the meta tag's post-insertion steps, which
+  // has the script-observable change to the default style sheet.
+  const postScript = document.createElement("script");
+  postScript.textContent = `
+    computedStyleInPostScript = getComputedStyle(div).display;
     scriptRan = true;
   `;
+
   const df = document.createDocumentFragment();
-  df.appendChild(script);
-  df.appendChild(meta);
-  assert_equals(getComputedStyle(div).display, "block", "div has block display");
+  df.append(preScript, meta, postScript);
+
+  assert_equals(getComputedStyle(div).display, "block",
+      "div still has block display before meta insertion");
   assert_false(scriptRan, "script has not run before insertion");
+
   document.head.appendChild(df);
   assert_true(scriptRan, "script has run after insertion");
-  assert_equals(computedStyleDuringInsertion, "none",
-      "display: none; style was applied during DOM insertion, before " +
-      "later-inserted script runs");
+  assert_equals(computedStyleInPreScript, "block",
+      "display: none; style was NOT applied during DOM insertion steps, " +
+      "before earlier-inserted script post-insertion steps run");
+  assert_equals(computedStyleInPostScript, "none",
+      "display: none; style WAS applied during DOM post-insertion steps, " +
+      "before later-inserted script runs");
   assert_equals(getComputedStyle(div).display, "none",
       "style remains display: none; after insertion");
+
 }, "Inserting <meta> that uses alternate stylesheets, applies the style " +
-   "during DOM insertion, and before script runs as a result of any atomic insertions");
+   "during DOM post-insertion steps");
 </script>