P3 M65? Sounds like this needs to be re-prioritized :P

May as well assign to myself while I'm here.  I'll probably address with a few other metrics cleanup at the same time.

Moving out, will try to clean up this milestone.

VrUsageMonitor no longer exists. What is the new name? Also, is this specific to VR browsing or all of XR?

All of xr.  

In chrome/browser/vr/metrics/session_metrics_helper.cc, SessionTimerImpl is the templated class, which uses UMA_HISTOGRAM_CUSTOM_TIMES and templates to get different instances of each session type.

Using base::UmaHistogramCustomTimes directly instead of the macro will avoid the templates and probably make this code easier to understand.