As of https://chromium-review.googlesource.com/c/chromium/src/+/641633 we include timing updates from all child frames.

However, this includes injected extension frames, which we don't want to track, as they could skew metrics (consider an extension that injects a frame in every page immediately after commit - this would report very fast times to first paint for every page load, which isn't what we're interested in measuring and would skew results).

For the time being we'll ignore all updates from extension frames.