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.

return element;
    }
    var container = document.createElement('div');
    ReactDOM.render(<Foo />, container);
    expectNoWaste(() => {
      element = null;
      ReactDOM.render(<Foo />, container);
    });
  });
  it('should include stats for components unmounted during measurement', function() {
    var container = document.createElement('div');
    var measurements = measure(() => {
      ReactDOM.render(<Div><Div key="a" /></Div>, container);
      ReactDOM.render(<Div><Div key="b" /></Div>, container);
    });
    expect(ReactPerf.getExclusive(measurements)).toEqual([{
      key: 'Div',
      instanceCount: 3,
      counts: { ctor: 3, render: 4 },