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.

childArray[i] = arguments[i + 2];
    }
    props.children = childArray;
  }
  return ReactElement(
    element.type,
    key,
    ref,
    self,
    source,
    owner,
    props
  );
};
/**
 * Verifies the object is a ReactElement.
 * See https://facebook.github.io/react/docs/top-level-api.html#react.isvalidelement
 * @param {?object} object
 * @return {boolean} True if `object` is a valid component.
 * @final
 */
ReactElement.isValidElement = function(object) {
  return (
    typeof object === 'object' &&
    object !== null &&
    object.$$typeof === REACT_ELEMENT_TYPE
  );
};
module.exports = ReactElement;