You might be referring to the Spectre mitigation changes:
Timer precision from performance.now and other sources is reduced to 1ms (r226495)
https://webkit.org/blog/8048/what-spectre-and-meltdown-mean-...
Timer precision from performance.now and other sources is reduced to 1ms (r226495)
https://webkit.org/blog/8048/what-spectre-and-meltdown-mean-...