[css-grid] Applying 'align-content' content distribution to row estimation in step 1 in Grid Sizing algo

[MatsPalmgren]

Follow-up from #2557.

The row size estimation for step 1 mentions "if any row with a definite max track sizing function had that size and all other rows were infinite". I tend to think this implies that if all rows have a definite max track sizing function, and the container has a definite block-size, that align-content should be applied. @javifernandez' example in #2557:

<div style="display: inline-grid; grid-template-rows: 50px 50px; height: 200px;  font: 20px/1 Ahem; justify-content: start; align-content: space-between;">
   <div style="grid-row: span 2; background: cyan; writing-mode: vertical-lr">XXX XX X XX X XXX</div>
</div>

should render exactly the same as if we add grid-row-gap:100px:

<div style="display: inline-grid; grid-template-rows: 50px 50px; grid-row-gap:100px; height: 200px;  font: 20px/1 Ahem; justify-content: start; align-content: space-between;">
   <div style="grid-row: span 2; background: cyan; writing-mode: vertical-lr">XXX XX X XX X XXX</div>
</div>

So I propose we add align-content content distribution for this specific case (all rows have definite max size) to the row estimation heuristics for step 1.

[fantasai]

Sounds good to me. Agenda+ for objections. :)

[css-meeting-bot]

The Working Group just discussed end, and agreed to the following:

• RESOLVED: Accept proposal in https://github.com/w3c/csswg-drafts/issues/2697

The full IRC log of that discussion

<dael> Topic: end
<dael> github: https://github.com//issues/2697
<dael> fantasai: I think this is a matter of getting it correct
<dael> astearns: Additional comments?
<dael> astearns: Objections to accepting https://github.com//issues/2697 or do people need time?
<dael> RESOLVED: Accept proposal in https://github.com//issues/2697

[fantasai]

Fix checked in. Let me know if there are any errors!