Browser optimizations and timeOrigin SpeedMetrics changelog
Change-Id: Ifb07bad4cdef71fdeede1cb33cb4d8099c4b7d80
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3555973
Reviewed-by: Mike Wittman <[email protected]>
Commit-Queue: Yoav Weiss <[email protected]>
Cr-Commit-Position: refs/heads/main@{#989420}
diff --git a/docs/speed/metrics_changelog/2022_03_lcp_fcp.md b/docs/speed/metrics_changelog/2022_03_lcp_fcp.md
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+# Loading metrics changes in Chrome 99
+
+## Navigation optimizations
+
+A few changes are being rolled out that may impact loading metrics, such as
+FCP and LCP. Most of these changes are
+[browser optimizations](https://blog.chromium.org/2022/03/a-new-speed-milestone-for-chrome.html)
+that should improve those loading metrics for everyone.
+
+## `timeOrigin` to take pre-`beforeUnload` IPC into account
+
+We also improved the accuracy of the `timeOrigin` value, on which all loading
+metrics are based. It now [takes into account an extra IPC call that happens
+before `beforeUnload` event handlers](https://bugs.chromium.org/p/chromium/issues/detail?id=1288485).
+In scenarios where traffic to your site is coming from a site with a
+`beforeUnload` handler, your timeline metrics are likely to slightly change:
+because the `timeOrigin` value is now earlier, durations relative to
+`timeOrigin` will appear to be larger.
+
+Note that the duration of the `beforeUnload` event itself is not included in
+the `timeOrigin`, as its semantic meaning is not changed.
+
+## How does this affect a site's metrics?
+On the whole, users will see significant improvements to both FCP and LCP due
+to this effort.
+
+The pre-`beforeUnload` IPC change means that if large parts of the traffic to
+your site are coming from sites with a `beforeUnload` handler, you may see a
+mix of metric regressions and progressions.
+Otherwise, you're likely to see your metrics improve.
+
+## When were users affected?
+This change is being rolled out starting from Chrome 99.
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diff --git a/docs/speed/metrics_changelog/fcp.md b/docs/speed/metrics_changelog/fcp.md
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This is a list of changes to [First Contentful Paint](https://web.dev/fcp).
+* Chrome 99
+ * Implementation optimizations: [Navigation optimizations and timeOrigin changes](2022_03_lcp_fcp_fid.md)
* Chrome 94
* Metric definition improvement: [Paint timing is only reported when the painted content
is not under opacity:0](2021_07_fcp.md)
diff --git a/docs/speed/metrics_changelog/lcp.md b/docs/speed/metrics_changelog/lcp.md
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This is a list of changes to [Largest Contentful Paint](https://web.dev/lcp).
+* Chrome 99
+ * Implementation optimizations: [Navigation optimizations and timeOrigin changes](2022_03_lcp_fcp_fid.md)
* Chrome 98
* Metric bug fix: [Text paints are more accurate](2021_11_lcp.md)
* Chrome 96
