Multiple WebVTT tests are flakily failing in the same way, with expected image being all white, and actual image being all black. This happens on Mountain Lion and Mavericks, see e.g. http://build.webkit.org/results/Apple%20MountainLion%20Debug%20WK2%20(Tests)/r167059%20(17098)/results.html
This makes EWS very slow and confused, I'm going to skip all that I see being flaky.
These tests don't work anyway - the content that's being tested is outside 800x600 snapshot area, so even when passing, all they confirm is that 800x600 white rectangle matches a 800x600 white rectangle.
> actual image being all black
That's not the problem we were seeing elsewhere though - the test visibly blinks black when loading in browser, so the snapshot is just taken at a wrong moment, it's not a complete failure taking it.
Skipped the test in <http://trac.webkit.org/r167065>.