In 263731@main, we introduced `LayoutTests/fast/canvas/offscreen-clipped.html` and its relative reftest expectation file; this test was marked failing immediately in GTK port. (Since then, it's been moved up to GLIB TestExpectations, since it also fails in WPE.)
(Sorry if I added the wrong people on this bug, it may just be functionality we are missing in GTK/WPE.)