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.

var c = 3;
    var element = React.createFactory(ComponentClass)(null, a, b, c);
    expect(element.props.children).toEqual([1, 2, 3]);
    expect(console.error.calls.count()).toBe(0);
  });
  
  
  it('allows static methods to be called using the type property', () => {
    spyOn(console, 'error');
    var StaticMethodComponentClass = React.createClass({
      statics: {
        someStaticMethod: function() {
          return 'someReturnValue';
        },
      },
      getInitialState: function() {
        return {valueToReturn: 'hi'};
      },
      render: function() {
        return React.createElement('div');
      },
    });
    var element = React.createElement(StaticMethodComponentClass);
    expect(element.type.someStaticMethod()).toBe('someReturnValue');
    expect(console.error.calls.count()).toBe(0);
  });
  
  
  it('identifies valid elements', () => {
    var Component = React.createClass({