PSA: JSON.stringify has changed behavior wrt DOM objects in Chrome

There's been a change in the behavior of recent (canary) versions of 
Chrome, described here:

https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/H0MGw0jkdn4/discussion

The change means that a lot of DOM attributes are now no longer picked 
up by JSON.stringify; I'm not quite sure whether this was intentional or 
not.

This affects a couple of examples in our spec that use JSON.stringify.
I've filed #204 to deal with the issue.

Harald