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Test Info:

<!DOCTYPE html>
<title>A smooth scroll operation in load event handler isn't omitted</title>
<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="support/scroll-behavior.js"></script>
<style>
body {
margin: 0;
}
html {
overflow: auto;
}
</style>
<div id="pageContent" style="position: absolute; left: 0; top: 0;"></div>
<script>
window.addEventListener("load", () => {
// Expand the page content to make the root scroll container overflowed.
pageContent.style.width = (window.innerWidth) * 5 + "px";
pageContent.style.height = (window.innerHeight) * 6 + "px";
promise_test(async () => {
document.scrollingElement.scrollTo({
left: window.innerWidth,
top: window.innerHeight,
behavior: "smooth"
});
assert_equals(document.scrollingElement.scrollLeft, 0, "Should not set scrollLeft immediately");
assert_equals(document.scrollingElement.scrollTop, 0, "Should not set scrollTop immediately");
// In the next frame, change something to trigger a paint which might
// clobber the smooth scroll operation.
await new Promise(resolve => requestAnimationFrame(resolve));
pageContent.style.color = "green";
await waitForScrollEnd(document.scrollingElement);
assert_equals(document.scrollingElement.scrollLeft, window.innerWidth, "Final value of scrollLeft");
assert_equals(document.scrollingElement.scrollTop, window.innerHeight, "Final value of scrollTop");
}, `Smooth scroll in load event handler`);
});
</script>