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Fix first visible timestamp and LCPV #37144

Merged
merged 2 commits into from
Dec 7, 2021
Merged

Fix first visible timestamp and LCPV #37144

merged 2 commits into from
Dec 7, 2021

Commits on Dec 7, 2021

  1. Fix first visible timestamp 

    In ampproject#36273, I switched from `Date.now()` to `performance.now()`, thinking it was a higher resolution timestamp time since the unix epoch. But, `peformance.now` is relative to _page load time_ (or `timeOrigin`), not the epoch.

This matters because our "since visible" metrics use the epoch as their base time, meaning the timestamps are roughly 1.6 trillion milliseconds. But `performance.now` is tiny, in the range of a few million for a page that was loaded an hour ago. When we calculated the "since visible", we received values that were still in the trillions when we expect millions.

By adding `performance.now()` and `performance.timeOrigin`, we get a timestamp relative to the epoch. Now when we calculate the "since visible", we get the correct values.
    @jridgewell
    jridgewell committed Dec 7, 2021
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  2. Update tests

    @jridgewell
    jridgewell committed Dec 7, 2021
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