572604 - Don't flush layout before firing onload except when necessary

Status: RESOLVED FIXED

(Core :: Layout, defect)

Description

[Jesse Ruderman]

Attachment: irc conversation

It would be nice to fire onload as soon as all script-observable effects are ready.  In particular, we generally don't need to flush layout, only style.  By avoiding a layout flush, we can save time overall if the onload script causes DOM/style changes.

The one case that requires flushing layout is if there are web fonts that we *might* have to load depending on the text.  We should be able to detect that case cheaply and only flush layout before onload in that case.

Pre-requisites:
* Make nsStyleSet say whether there are any font-face rules (should be easy)
* Fix talos (?)

Comment 1

[Boris Zbarsky [:bzbarsky]]

Attachment: Like so

Comment 2

[Boris Zbarsky [:bzbarsky]]

I'd really like to land this as soon after b2 as possible so it can bake...

Comment 3

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Comment on attachment 456500 [details] [diff] [review]
Like so

Getting to this point means that we've already parsed all the style sheets?  (We don't need to flush anything in order to ensure that?)

If so, r=dbaron.

Comment 4

[Boris Zbarsky [:bzbarsky]]

> Getting to this point means that we've already parsed all the style sheets? 

Yes.

Comment 5

[Boris Zbarsky [:bzbarsky]]

Pushed http://hg.mozilla.org/mozilla-central/rev/a2c9de706e86

Then pushed http://hg.mozilla.org/mozilla-central/rev/3687d3cf3176 to bump assertion counts on one test that ended up asserting more of the same things it was already asserting.