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

**What is the current behavior?**
This addresses a bug in `enzyme`, https://github.com/airbnb/enzyme/issues/1683.

On [this line](https://github.com/facebook/react/blob/master/packages/react-test-renderer/src/ReactShallowRenderer.js#L110) `element.type()` invokes the SFC with `element` as the `this` value. I believe that this is needed for create-react-class components, but that there needs to be a separate branch for SFCs.

**What is the expected behavior?**
`this` inside a strict-mode SFC will be `undefined`, not the element.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
In all of React 0.13, 0.14, 15, and 16, this bug exists.

While the bug ideally will be fixed, I understand that it's highly unlikely that it would be backported to the 14/15 lines - but I can wrap around it if there's a reliable way, in those versions, to distinguish SFCs from create-react-class components (is there?).
element.type.contextTypes,
            this._context,
            'context',
            getName(element.type, this._instance),
            getStackAddendum,
          );
          currentlyValidatingElement = null;
        }
        this._mountClassComponent(element, this._context);
      } else {
        this._rendered = element.type(element.props, this._context);
      }
    }
    this._rendering = false;
    this._updater._invokeCallbacks();
    return this.getRenderOutput();
  }
  unmount() {
    if (this._instance) {
      if (typeof this._instance.componentWillUnmount === 'function') {
        this._instance.componentWillUnmount();
      }
    }
    this._context = null;
    this._element = null;
    this._newState = null;
    this._rendered = null;
    this._instance = null;
  }
  _mountClassComponent(element, context) {