Honor will-change: position dynamic changes.
Differential Revision: https://phabricator.services.mozilla.com/D9032
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1499863
gecko-commit: 2dd8df3604ef3a4130daea876a25efe6db16536f
gecko-integration-branch: autoland
gecko-reviewers: dbaron
diff --git a/css/css-will-change/will-change-abspos-cb-dynamic-001.html b/css/css-will-change/will-change-abspos-cb-dynamic-001.html
new file mode 100644
index 0000000..d250325
--- /dev/null
+++ b/css/css-will-change/will-change-abspos-cb-dynamic-001.html
@@ -0,0 +1,34 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>CSS Test: will-change: position turns an element in an abspos containing block when changed dynamically.</title>
+<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
+<link rel="author" title="Mozilla" href="https://mozilla.org">
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1499863">
+<link rel="help" href="https://drafts.csswg.org/css-will-change/#will-change">
+<link rel="match" href="will-change-abspos-cb-001-ref.html">
+<style>
+ .container {
+ border: 1px solid green;
+ width: 100px;
+ height: 100px;
+ margin-top: 100px;
+ }
+ .abspos {
+ position: absolute;
+ top: 0;
+ left: 0;
+ background: orange;
+ height: 20px;
+ width: 20px;
+ }
+</style>
+<div class="container">
+ <div class="abspos"></div>
+</div>
+<script>
+onload = function() {
+ let container = document.querySelector(".container");
+ container.offsetTop;
+ container.style.willChange = "position";
+}
+</script>
