Using performance.mark/performance.measure makes it much easier to take a look at the profiler data because it also creates markers for these events automatically. That way users can easily take a look at the profile data to analyze it. It's important for having more actionable profiles.

During the discussion we had in the performance work week, we discussed that we can also keep the performance.now and add markers with ChromeUtils.addProfilerMarker. The reason behind using ChromeUtils is the performance advantage compared to using performance.mark/measure. I will look at our performance.now usages and overhead of using performance.mark/measure instead and decide what to use.