**Do you want to request a *feature* or report a *bug*?**

Bug

**What is the current behavior?**

Calling `this.isMounted()` in `componentWillUnmount` in prior versions would return `true`. Now it returns `false`.

I believe this was untested behavior before, but the new tests that were added may check the wrong value: https://github.com/facebook/react/blob/master/src/isomorphic/classic/class/__tests__/create-react-class-integration-test.js#L417 Changing this line to test for `true` will exhibit the behavior.

The fix would be to defer setting the  `__isMounted` flag to `false` until after all mixins and the `componentWillUnmount` method were called on the component.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

15.5.x and anything using `create-react-class` is broken. Working correctly in 15.4.x with `React.createClass`.

ops.push(`${name}: ${this.isMounted()}`);
      },
      getInitialState() {
        this.log('getInitialState');
        return {};
      },
      componentWillMount() {
        this.log('componentWillMount');
      },
      componentDidMount() {
        this.log('componentDidMount');
      },
      componentWillUpdate() {
        this.log('componentWillUpdate');
      },
      componentDidUpdate() {
        this.log('componentDidUpdate');
      },
      componentWillUnmount() {
        this.log('componentWillUnmount');
      },
      render() {