There is a bug in the logic for determining if `props` is a plain object. This bug results in a false positive, flooding the console with hundreds of instances of this warning: "Expected props argument to be a plain object. Properties defined in its prototype chain will be ignored.".

The code that's failing is in [ReactElement.js, Line 210 in the v15.3.1 branch](https://github.com/facebook/react/blob/v15.3.1/src/isomorphic/classic/element/ReactElement.js#L210) (line number is probably different in master)

> config.**proto** == null || config.**proto** === Object.prototype,

This fails when the props object is created in one iframe, but uses an instance of React from another frame. Each browser window/tab/frame has it's own instance of the Object constructor. For instance, `document.querySelector('iframe').contentWindow.Object === Object` always results in `false`.

Check out this [demo](https://jsfiddle.net/05ugxo5f/4/), which shows the false-positive warning message.

});
  
  
  it('is indistinguishable from a plain object', () => {
    var element = React.createElement('div', {className: 'foo'});
    var object = {};
    expect(element.constructor).toBe(object.constructor);
  });
  
  
  it('should use default prop value when removing a prop', () => {
    var Component = React.createClass({
      getDefaultProps: function() {
        return {fruit: 'persimmon'};
      },
      render: function() {
        return React.createElement('span');
      },
    });
    var container = document.createElement('div');
    var instance = ReactDOM.render(
      React.createElement(Component, {fruit: 'mango'}),
      container
    );
    expect(instance.props.fruit).toBe('mango');
    ReactDOM.render(React.createElement(Component), container);
    expect(instance.props.fruit).toBe('persimmon');
  });