IFrame in fixed div scrolls down with page, when it should stay fixed.

[samuknet]

When an IFrame is in a fixed div container, scrolling down the page causes the IFrame to be 'scrolled' too, when it should remain in place due the div being CSS position:fixed;

Online test case here.

[jdm]

Note, this only reproduces without webrender enabled. I filed #13015 about how webrender breaks this in totally different ways.

[glennw]

I can't reproduce #13015 with webrender - it seems to work correctly. But this bug seems to occur the same both with/without webrender enabled for me. I'll look into it today.

[glennw]

Will be fixed in WR when servo/webrender#368 lands in master.

[glennw]

Fixed as part of #13099