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Test Info:

<!DOCTYPE html>
<html class="reftest-wait reftest-no-flush">
<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
<!--
A test for a partial pre-rendered transform animation moves to a place where
the whole area of the transform animation is out of the viewport.
We consider it jank, thus we report it to the main-thread, then we clear out
the initial green rectangle, thus the result should be a blank page.
-->
<style>
html {
overflow: hidden;
}
body {
margin: 0px;
padding: 0px;
}
@keyframes anim {
/* translate to a position the element is completely outside of the */
/* viewport */
to { transform: translateX(-300vw); }
}
#target {
width: 200vw;
height: 200vh;
position: absolute;
/* Some part of this element needs to be visible initially so that */
/* a display item for this element is generated, thus the transform */
/* animation runs on the compositor. */
transform: translateX(-110vw);
}
</style>
<div id="target">
<!--
Put an SVG element so that the transform display item has a blob on
WebRender which means this test properly fails without the proper fix.
-->
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16">
<rect fill="green" width="16" height="16"></rect>
</svg>
</div>
<script>
document.addEventListener("MozReftestInvalidate", () => {
target.style.animation = "anim 100s 1s step-start";
target.addEventListener("animationstart", () => {
// Wait 100ms to make sure we can report the jank to the main-thread and
// in response to the report we can do a paint process on the main-thread.
setTimeout(() => {
document.documentElement.classList.remove("reftest-wait");
}, 100);
});
}, { once: true });
</script>
</html>