The background-size interactive test includes a test-case which uses the
ClutterActor::paint signal to hijack the painting of the actor. We're
removing that signal from Clutter, so remove that signal handler and
paint the outer border unconditionally to mark the boundaries of the
widget (the outer border actually never worked to force the cairo/cogl
path). To fix the test, change it to not paint a border on the inner
container in the useCairo=false case, which should make sure the cogl
path gets used.
Also remove the useless useCairo argument from addTestLine().
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1479
012af56b37