There's a TODO rkaplow to do this if they turn out to look similar enough: https://cs.chromium.org/chromium/src/chrome/browser/extensions/installed_loader.cc?q=%5C"Extensions.LoadAllTime&sq=package:chromium&l=317&dr=C

Looks like they do: https://uma.googleplex.com/p/chrome/histograms/?endDate=07-05-2016&dayCount=1&histograms=Extensions.LoadAllTime%2CExtensions.LoadAllTime2&fixupData=true&showMax=true&filters=channel%2Ceq%2C4%2Cisofficial%2Ceq%2CTrue&implicitFilters=isofficial