Layout shift detection for fixed position

With paint properties geometry mapping, we can already correctly detect layout shift of fixed-position elements because the viewport scroll offset doesn't exist in the paint property chain of fixed-position elements. Also removed the unnecessary layout viewport clip because it's already applied in LocalToAncestorClipRect to the LayoutView property tree state. Change-Id: I0d77bb4fc828b495536b03f8674d8cab35d0f8bd Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2520330 Reviewed-by: Steve Kobes <skobes@chromium.org> Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org> Cr-Commit-Position: refs/heads/master@{#824480}
web-platform-tests · Nov 5, 2020 · 3a36f4a · 3a36f4a
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diff --git a/layout-instability/fixed-position-move.html b/layout-instability/fixed-position-move.html
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+<!DOCTYPE html>
+<title>Layout Instability: movement of fixed position</title>
+<link rel="help" href="https://wicg.github.io/layout-instability/" />
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/util.js"></script>
+<div id="target" style="position: fixed; top: 100px; width: 300px; height: 200px; background: yellow">
+</div>
+<script>
+promise_test(async () => {
+  const watcher = new ScoreWatcher;
+
+  // Wait for the initial render to complete.
+  await waitForAnimationFrames(2);
+
+  // Modify the position of the div.
+  target.style.top = '200px';
+
+  const expectedScore = computeExpectedScore(300 * (200 + 100), 100);
+
+  // Observer fires after the frame is painted.
+  assert_equals(watcher.score, 0);
+  await watcher.promise;
+  assert_equals(watcher.score, expectedScore);
+}, 'Movement of fixed position');
+
+</script>