Support oncontentvisibilityautostatechange event handler

Spec PR: whatwg/html#10364

Differential Revision: https://phabricator.services.mozilla.com/D217187

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1898833
gecko-commit: e2635b8bf747fe8542ea4442db5aca85bd94eb1b
gecko-reviewers: emilio, smaug

css/css-contain/content-visibility/content-visibility-auto-state-changed.html

@@ -24,16 +24,22 @@
 
 <script>
 let contentattrfired = false;
+let contentattrfiredonsvg = false;
 
 function contentattrDidFire() {
   contentattrfired = true;
 }
 
+function contentattrDidFireOnSvg() {
+  contentattrfiredonsvg = true;
+}
+
 </script>
 
 <div id=upper></div>
 <div id=attrtest></div>
 <div id=contentattrtest oncontentvisibilityautostatechange="contentattrDidFire()" class=auto></div>
+<svg id="svgcontentattrtest" oncontentvisibilityautostatechange="contentattrDidFireOnSvg()" class="auto"></svg>
 <div class=spacer></div>
 <div id=middle></div>
 <div class=spacer></div>
@@ -83,6 +89,12 @@
   assert_true(contentattrfired, "contentattrfired");
 }, "ContentVisibilityAutoStateChange content attribute test");
 
+
+promise_test(async t => {
+  await waitForAtLeastOneFrame();
+  assert_true(contentattrfiredonsvg, "contentattrfiredonsvg");
+}, "ContentVisibilityAutoStateChange content attribute test on svg");
+
 promise_test(t => new Promise(async (resolve, reject) => {
   await new Promise((waited, _) => {
     requestAnimationFrame(() => requestAnimationFrame(waited));