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-rw-r--r--testing/web-platform/tests/largest-contentful-paint/placeholder-image.html31
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diff --git a/testing/web-platform/tests/largest-contentful-paint/placeholder-image.html b/testing/web-platform/tests/largest-contentful-paint/placeholder-image.html
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+++ b/testing/web-platform/tests/largest-contentful-paint/placeholder-image.html
@@ -0,0 +1,31 @@
+<!DOCTYPE HTML>
+<meta charset=utf-8>
+<title>Largest Contentful Paint: src change triggers new entry.</title>
+<body>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/largest-contentful-paint-helpers.js"></script>
+<img src='/images/green-1x1.png' id='image_id' width="133" height="106"/>
+<script>
+ async_test(function (t) {
+ assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
+ let beforeLoad = performance.now();
+ document.getElementById('image_id').src = '/images/blue.png';
+ const url = window.location.origin + '/images/blue.png';
+ const observer = new PerformanceObserver(
+ t.step_func(function(entryList) {
+ let entries = entryList.getEntries().filter(e => e.url === url);
+ if (entries.length === 0)
+ return;
+ assert_equals(entries.length, 1);
+ const entry = entries[0];
+ // blue.png is 133 by 106.
+ const size = 133 * 106;
+ checkImage(entry, url, 'image_id', size, beforeLoad);
+ t.done();
+ })
+ );
+ observer.observe({type: 'largest-contentful-paint', buffered: true});
+ }, 'Largest Contentful Paint: changing src causes a new entry to be dispatched.');
+</script>
+</body>