753777 - ringmark's matchMedia test fails because we don't flush to create presContext for newly-created iframe

Status: RESOLVED FIXED

Description

[David Baron :dbaron: ⌚️UTC-7]

Steps to reproduce:
 1. load http://rng.io/?all and let it run
 2. open Ring 1
 3. open 2D Games
 4. open CSS3 MediaQueries
 5. look at the results

Actual results: second and third tests fail

Expected results: all tests pass

What's happening here is that we're failing this null-check:
http://hg.mozilla.org/mozilla-central/file/6fe7dd2f8f57/dom/base/nsGlobalWindow.cpp#l3817
because presContext is null.

If I add a FlushPendingNotifications(Flush_Layout) call earlier in the method, the tests pass.

The question is whether there's any weaker flush (e.g., flush on the parent) that would be sufficient to ensure that nsGlobalWindow::GetPresContext gives an up-to-date result.

Comment 1

[Boris Zbarsky [:bz]]

I _think_ that a Flush_Style on the parent should be sufficient if we don't care about having the prescontext size up to date.

Comment 2

[David Baron :dbaron: ⌚️UTC-7]

Er, I meant to do Flush_Frames and then I did Flush_Layout for some reason.

I think we do need the size up-to-date, though, and I *think* something deeper in the code does a flush to ensure that, though I need to check.

Comment 3

[Boris Zbarsky [:bz]]

OK.  Worst case, a Flush_Layout on the parent would suffice; nsGlobalWindow even has an EnsureSizeUpToDate helper for that.

Comment 4

[David Baron :dbaron: ⌚️UTC-7]

nsDOMMediaQueryList actually doesn't have any flushes, but almost certainly needs them

Comment 5

[David Baron :dbaron: ⌚️UTC-7]

Created attachment 639487 [details] [diff] [review]
patch

Anyway, we should get this in.  comment 4 should be a separate bug.

Comment 6

[Boris Zbarsky [:bz]]

Comment on attachment 639487 [details] [diff] [review]
patch

r=me

Comment 7

[David Baron :dbaron: ⌚️UTC-7]

https://hg.mozilla.org/integration/mozilla-inbound/rev/70995c6989e4

Comment 8

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/70995c6989e4

Comment 9

[David Baron :dbaron: ⌚️UTC-7]

Filed bug 1011468 on comment 4.