function getUnchangedComponents(measurement) {
  // For a given reconcile, look at which components did not actually
  // render anything to the DOM and return a mapping of their ID to
  // the amount of time it took to render the entire subtree.
  var cleanComponents = {};
  var dirtyLeafIDs = Object.keys(measurement.writes);
  var allIDs = assign({}, measurement.exclusive, measurement.inclusive);

  for (var id in allIDs) {
    var isDirty = false;
    // For each component that rendered, see if a component that triggered
    // a DOM op is in its subtree.
    for (var i = 0; i < dirtyLeafIDs.length; i++) {
      if (dirtyLeafIDs[i].indexOf(id) === 0) {
        isDirty = true;
        break;
      }
    }
    if (!isDirty && measurement.counts[id] > 0) {
      cleanComponents[id] = true;
    }
  }
  return cleanComponents;
}
Base constructor for all React elements. This is only used to make this
work with a dynamic instanceof check. Nothing should live on this prototype.

@param {*} type
@param {string|object} ref
@param {*} key
@param {*} props
@internal