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+++ b/testing/web-platform/tests/largest-contentful-paint/larger-image.html
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+<!DOCTYPE HTML>
+<meta charset=utf-8>
+<title>Largest Contentful Paint: largest image is reported.</title>
+
+<body>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+  <script src="resources/largest-contentful-paint-helpers.js"></script>
+  <!-- There is some text and some images. We care about blue.png being reported, as it is the largest. -->
+  <p>This is some text! :)</p>
+  <img src='' id='red' />
+  <img src='' id='blue' />
+  <img src='' id='black' />
+  <p>More text!</p>
+  <script>
+    // Add listener for load event that is fired when image is loaded.
+    function image_load_promise(image_element) {
+      return new Promise(resolve => {
+        image_element.addEventListener('load', resolve);
+      });
+    }
+
+    promise_test(async (t) => {
+      assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
+
+      let promise = image_load_promise(document.getElementById('red'));
+      document.getElementById('red').src = '/images/red.png';
+      await promise;
+
+      const beforeLoad = performance.now();
+
+      promise = image_load_promise(document.getElementById('blue'));
+      document.getElementById('blue').src = '/images/blue.png';
+      await promise;
+
+      promise = image_load_promise(document.getElementById('black'));
+      document.getElementById('black').src = '/images/black-rectangle.png';
+      await promise;
+
+      const observer = new PerformanceObserver(
+        t.step_func(entryList => {
+          entryList.getEntries().forEach(entry => {
+            // The text or other image could be reported as LCP if it is rendered before the blue image.
+            if (entry.id !== 'blue')
+              return;
+
+            const url = window.location.origin + '/images/blue.png';
+            // blue.png is 133 by 106.
+            const size = 133 * 106;
+            checkImage(entry, url, 'blue', size, beforeLoad);
+            t.done();
+          })
+        })
+      );
+      observer.observe({ type: 'largest-contentful-paint', buffered: true });
+    }, 'Largest Contentful Paint: largest image is reported.');
+  </script>
+</body>