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.

console.table = () => {};
      console.table.isFake = true;
    }
    React = require('React');
    ReactDOM = require('ReactDOM');
    ReactPerf = require('ReactPerf');
    ReactTestUtils = require('ReactTestUtils');
    App = React.createClass({
      render: function() {
        return <div><Box /><Box flip={this.props.flipSecond} /></div>;
      },
    });
    Box = React.createClass({
      render: function() {
        return <div key={!!this.props.flip}><input /></div>;
      },
    });
    
    Div = React.createClass({
      render: function() {
        return <div {...this.props} />;
      },
    });
  });
  afterEach(function() {
    if (console.table.isFake) {
      delete console.table;
    }
  });
  function measure(fn) {