JFR: Do we want to build histograms based on both grouped thread and class?

[kittylyst]

Currently, AbstractThreadDispatchingHandler looks at incoming JFR events and delegates them based on the (grouped) thread name.

Some JFR events, e.g. jdk.JavaMonitorWait also have a monitorClass that might be a useful attribute (and potentially a stack trace, but that's another story!)

We could prototype a new abstract base that considers both the class name and thread name of the incoming event and segregates the histograms. Without seeing this in practice, I'm not sure how useful the dual attributes will be.