Hover Preview inconsistency: no preview / empty preview for unsupported gradients

[peterflynn]

Hover over each of the following:

.foo {
    background-image: linear-gradient(to right, #333, #CCC);
    background-image: -webkit-radial-gradient(center center, circle contain, black 0%, blue 25%, green 40%, red 60%, purple 80%, white 100%);
    background-image: -moz-radial-gradient(center center, circle contain, black 0%, blue 25%, green 40%, red 60%, purple 80%, white 100%);  
    background-image: radial-gradient(yellow, green); 
    background-image: repeating-linear-gradient(red, blue 20px, red 40px);
    background-image: repeating-radial-gradient(red, blue 20px, red 40px);
}

Result:
Hover preview appears for the first three, but is blank (empty checkerboard). Hover preview does not appear for the last two.

Expected:
Should we be more consistent? It seems better to not show a preview for unsupported cases rather than to show a preview that's incorrect. But how hard is it to detect which cases are supported?

[peterflynn]

Tentatively assigning to Sprint 24 -- we should at least think about what we want to do about this.

[peterflynn]

Note: I'm going to disable some of the Hover Preview unit tests that depend on the answer to this. We should re-enable them once the expected result is decided.

[peterflynn]

Pull request #3482 may fix this -- still need to verify.

[peterflynn]

Fixed by #3482 -- the two prefixed radial gradients now work, and the remaining cases don't show a preview at all.