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.

emitEvent('onEndProcessingChildContext');
  },
  onHostOperation(debugID, type, payload) {
    checkDebugID(debugID);
    emitEvent('onHostOperation', debugID, type, payload);
  },
  onSetState() {
    emitEvent('onSetState');
  },
  onSetDisplayName(debugID, displayName) {
    checkDebugID(debugID);
    emitEvent('onSetDisplayName', debugID, displayName);
  },
  onSetChildren(debugID, childDebugIDs) {
    checkDebugID(debugID);
    emitEvent('onSetChildren', debugID, childDebugIDs);
  },
  onSetOwner(debugID, ownerDebugID) {
    checkDebugID(debugID);
    emitEvent('onSetOwner', debugID, ownerDebugID);
  },
  onSetText(debugID, text) {
    checkDebugID(debugID);
    emitEvent('onSetText', debugID, text);
  },
  onMountRootComponent(debugID) {
    checkDebugID(debugID);
    emitEvent('onMountRootComponent', debugID);
  },
  onMountComponent(debugID) {