css/css-backgrounds/animations/border-image-source-interpolation.html has failures

[Antoine Quint]

css/css-backgrounds/animations/border-image-source-interpolation.html has 50 failures, we need to investigate and fix them.

[Radar WebKit Bug Importer]

<rdar://problem/88488364>

[Karl Dubost]

Antoine,

These failures are weird.
They happen mostly when

"border-image-source" is set 
* from "inherit" 
* to something else

and the window.getComputedStyle value returns a surprising "cross-fade()"

For example:

CSS Transitions and CSS Animations
<border-image-source> 
from [inherit] 
to [url(http://wpt.live/support/orange_color.png)] at (-0.3) 
should be [url(http://wpt.live/support/orange_color.png)]

but it returns 
cross-fade(
  url(http://wpt.live/support/green.png), 
  url(http://wpt.live/support/orange_color.png), 
  -0.3
  )

Why the cross-fade() ?
This happens only when the starting value is inherit and different from 0


For inherit and 0, it has a different error
expected: url(http://wpt.live/support/orange_color.png)
actual:   url(http://wpt.live/support/green.png)

For inherit and 1, they PASS

Web Animations seem to be mostly working apart of a couple of things.


CSS Animations tests
from image to image mostly fail in the intermediate steps (so except for 0 and 1 which is a PASS).

[Antoine Quint]

This is because we treat most of the image types in CSS as animatable when they are not. The `cross-fade()` value is a representation of blending two images. The issue is that WebKit feels those specs should be updated to make those properties animatable.