Add tests for exiting from nested fullscreen

third_party/WebKit/LayoutTests/external/wpt_automation/fullscreen/auto-click.js

 (function() {
 
+// Gets the offset of an element in coordinates relative to the top-level frame.
+function offset(element) {
+  const rect = element.getBoundingClientRect();
+  const iframe = element.ownerDocument.defaultView.frameElement;
+  if (!iframe)
+    return { left: rect.left, top: rect.top };

[Mike West, 2017/02/24 11:37:16]

I must be getting old, but the `{}` for the object confused me given the lack of
`{}` for the `if`. Would you mind terribly putting braces around the body here?

[foolip, 2017/02/24 15:12:58]

Ah, this does look a bit, more {} it is.

+  const style = getComputedStyle(iframe);

[Mike West, 2017/02/24 11:37:16]

I don't think you actually use this. Is it just to force a recalc?

[foolip, 2017/02/24 15:12:58]

It's used as style[prop] inside the get function.

+  function get(prop) {

[Mike West, 2017/02/24 11:37:16]

Hrm. I don't know if we have a style-guide about nested functions, but I'd
personally change this to something like:

```
var get = prop => +/[\d.]*/.exec(style[prop])[0];
```

[foolip, 2017/02/24 15:12:58]

Didn't think of that, done. (I also threw in some var->const)

+    return +/[\d.]*/.exec(style[prop])[0];
+  }
+  const outerOffset = offset(iframe);
+  return {
+    left: outerOffset.left + get('borderLeftWidth') + get('paddingLeft') + rect.left,
+    top: outerOffset.top + get('borderTopWidth') + get('paddingTop') + rect.top
+  };
+}
+
 function click(button) {
-  var rect = button.getBoundingClientRect();
-  eventSender.mouseMoveTo(rect.left, rect.top);
+  var pos = offset(button);
+  eventSender.mouseMoveTo(Math.ceil(pos.left), Math.ceil(pos.top));
   eventSender.mouseDown();
   eventSender.mouseUp();
 }
 
 var observer = new MutationObserver(mutations => {
   for (var mutation of mutations) {
     for (var node of mutation.addedNodes) {
       if (node.localName == 'button')
         click(node);
       else if (node.localName == 'iframe')
         observe(node.contentDocument);
     }
   }
 });
 
 function observe(target) {
   observer.observe(target, { childList: true, subtree: true });
 }
 
 // Handle what's already in the document.
 for (var button of document.getElementsByTagName('button')) {
   click(button);
 }
 for (var iframe of document.getElementsByTagName('iframe')) {
   observe(iframe.contentDocument);
+  iframe.addEventListener('load', () => {
+    observe(iframe.contentDocument);
+  });
 }
 
 // Observe future changes.
 observe(document);
 
 })();