I've tested the new Perf tools on one of the screens in one app I'm working on and it works great :)

One thing I wanted also on the old one Perf tools was to be able to check whether the Perf tools are started or stopped, so basically exposing `ReactDebugTool`'s `isProfiling` variable. My use for that is that I have a keyboard shortcut (in development) bound to start/stop the Perf tools and currently I'm forced to maintain such a variable myself to know whether to start or stop (which gets out of sync if I start/stop the perf tools without the keyboard shortcut).

If you don't think it's worthwhile to expose `isProfiling` feel free to close this issue.

checkDebugID(debugID);
    emitEvent('onBeginReconcilerTimer', debugID, timerType);
  },
  onEndReconcilerTimer(debugID, timerType) {
    checkDebugID(debugID);
    emitEvent('onEndReconcilerTimer', debugID, timerType);
  },
  onBeginProcessingChildContext() {
    emitEvent('onBeginProcessingChildContext');
  },
  onEndProcessingChildContext() {