Function callback

__tests__/ReactChildren-test.js:93–96

(kid, index)

  it('should invoke callback with the right context', function() {
    var lastContext;
    var callback = function(kid, index) {
      lastContext = this;
      return this;
    };

    // TODO: Use an object to test, after non-object fragments has fully landed.
    var scopeTester = 'scope tester';