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.

ReactComponentTreeDevtool.purgeUnmountedComponents();
  ReactHostOperationHistoryDevtool.clearHistory();
}
function getTreeSnapshot(registeredIDs) {
  return registeredIDs.reduce((tree, id) => {
    var ownerID = ReactComponentTreeDevtool.getOwnerID(id);
    var parentID = ReactComponentTreeDevtool.getParentID(id);
    tree[id] = {
      displayName: ReactComponentTreeDevtool.getDisplayName(id),
      text: ReactComponentTreeDevtool.getText(id),
      updateCount: ReactComponentTreeDevtool.getUpdateCount(id),
      childIDs: ReactComponentTreeDevtool.getChildIDs(id),
      
      ownerID: ownerID || ReactComponentTreeDevtool.getOwnerID(parentID),
      parentID,
    };
    return tree;
  }, {});
}
function resetMeasurements() {