Define Navigation Timing moments

[Ms2ger]

Navigation Timing has various phrases like

the time immediately before the user agent sets the current document readiness of the current document to "complete"

and

a time value equal to the time when the load event of the current document is completed

We should have the HTML Standard define those moments within the relevant algorithms, so NT can just defer to it.

CC @plehegar

[annevk]

I think @igrigorik has been planning on better Fetch integration too. I agree it would be good if all the performance work integrated with the larger "platform framework".

[igrigorik]

Some background:

1. Nav Timing L2 is now based on Resource Timing L2 (a navigation is "special" resource fetch)
2. We have an outstanding issue to redefine RT on top of Fetch: Define Resource Timing in terms of Fetch w3c/resource-timing#39 -- realistically, this is probably an "~L3" feature.
   • Once this is resolved, NT will inherit the logic as well.

Once we resolve (2), I think it makes sense to take a closer look at integration with HTML.

[domenic]

Fixed in d799c4c.