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('onMountComponent', debugID);
  },
  onUpdateComponent(debugID) {
    checkDebugID(debugID);
    emitEvent('onUpdateComponent', debugID);
  },
  onUnmountComponent(debugID) {
    checkDebugID(debugID);
    emitEvent('onUnmountComponent', debugID);
  },
  onTestEvent() {
    emitEvent('onTestEvent');
  },
};
if (__DEV__) {
  var ReactInvalidSetStateWarningDevTool = require('ReactInvalidSetStateWarningDevTool');
  var ReactHostOperationHistoryDevtool = require('ReactHostOperationHistoryDevtool');
  var ReactComponentTreeDevtool = require('ReactComponentTreeDevtool');
  ReactDebugTool.addDevtool(ReactInvalidSetStateWarningDevTool);
  ReactDebugTool.addDevtool(ReactComponentTreeDevtool);
  ReactDebugTool.addDevtool(ReactHostOperationHistoryDevtool);
  var url = (ExecutionEnvironment.canUseDOM && window.location.href) || '';
  if ((/[?&]react_perf\b/).test(url)) {
    ReactDebugTool.beginProfiling();
  }
}
module.exports = ReactDebugTool;