It isn't clear whether a document.open() as defined here:
https://html.spec.whatwg.org/multipage/webappapis.html#dom-document-open
http://www.w3.org/TR/html5/webappapis.html#dom-document-open
results in a new navigation entry. It seems desirable that it would, but the
HTML spec doesn't say that document.open() causes a 'navigation' that results in
running the steps at:
https://html.spec.whatwg.org/multipage/browsers.html#navigate
http://www.w3.org/TR/html5/browsers.html#navigate
From step 15 at the document.open text it seems that the PerformanceTiming
object will be replaced since the Window object that it hangs off of is
replaced. If a 'navigation' doesn't happen though, it's not clear what the
impact of document.open() is on the value of performance.timing.navigationStart
etc. or on the timing values on the new PerformanceNavigationTiming object.
I'm particularly interested in this because Web Animations relies on the value
of navigationStart.
