**Do you want to request a *feature* or report a *bug*?**
Bug

**What is the current behavior?**
In mobile Safari, DOM events originating from elements rendered through a Portal do **not** bubble (propagate) up the React component tree.

**If the current behavior is a bug, please provide the steps to reproduce....**
Please see the following JSFiddle: https://jsfiddle.net/zebulonj/wf7orwan/

In this JSFiddle, the expected behavior (seen in a desktop browser) is that clicking on the portal content (appearing as a modal, including backdrop) should toggle to the "On" or "Off" indicator rendered in the main content. However, in mobile Safari (iOS 11.1.1), the click events do not propagate.


**What is the expected behavior?**
Click events should propagate up the React component tree.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
Affected: React 16.2
iOS 11.1.1

parentInstance: Instance,
  child: Instance | TextInstance,
): void {
  parentInstance.appendChild(child);
}
export function appendChildToContainer(
  container: Container,
  child: Instance | TextInstance,
): void {
  if (container.nodeType === COMMENT_NODE) {
    (container.parentNode: any).insertBefore(child, container);
  } else {
    container.appendChild(child);
  }
}
export function insertBefore(
  parentInstance: Instance,
  child: Instance | TextInstance,
  beforeChild: Instance | TextInstance,
): void {
  parentInstance.insertBefore(child, beforeChild);
}
export function insertInContainerBefore(
  container: Container,
  child: Instance | TextInstance,
  beforeChild: Instance | TextInstance,
): void {
  if (container.nodeType === COMMENT_NODE) {