Web-Facing Change PSA: Corrected timing for low-lead-time prefetches

[Jeremy Roman]

Chrome 126 (and corresponding releases from other Chromium browser vendors) will reflect a bugfix to the reporting of the responseStart timestamp for speculation rules prefetched navigation. It may cause a shift in some metrics, notably an increase in computed time to first byte (or similar metrics) and a corresponding decrease in metrics measured from after the response body starts.

See this document for more detail:

https://docs.google.com/document/d/1oESLkgpXysbl_FQMZ5Ahj3xtHW6d_UTcB-StJrS7a1U/preview

This is intended as a bugfix, but I am mentioning it more broadly because of the potential to look a little confusing in real user metrics.