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.

it('should not count raw HTML update as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(
      <Div dangerouslySetInnerHTML={{__html: 'me'}} />,
      container
    );
    expectNoWaste(() => {
      ReactDOM.render(
        <Div dangerouslySetInnerHTML={{__html: 'you'}} />,
        container
      );
    });
  });
  it('should not count child reordering as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div><div key="A" /><div key="B" /></Div>, container);
    expectNoWaste(() => {
      ReactDOM.render(<Div><div key="B" /><div key="A" /></Div>, container);
    });
  });
  it('should not count text update as waste', function() {
    var container = document.createElement('div');
    ReactDOM.render(<Div>{'hello'}{'world'}</Div>, container);
    expectNoWaste(() => {
      ReactDOM.render(<Div>{'hello'}{'friend'}</Div>, container);
    });
  });
  it('should not count replacing null with a native as waste', function() {
    var element = null;
    function Foo() {