This came form the follow discussion on IRC:
6:19 PM <tonikitoo> smfr: since ScrollAnimator has hooks for when mouse enters/leaves/clicks an overlay scrollbar area.
6:20 PM <tonikitoo> These hooks are what behavior similarly with and without the patch.
6:22 PM <tonikitoo> I have not tried ref test yet, but have not seen recent overlay scrollbar changes come with tests.
6:22 PM <tonikitoo> smfr: Do you have any pointers?
6:22 PM <smfr> we probably need to make a way to say “draw scrollbars now for testing"
6:23 PM <smfr> s/draw/make visible/
6:23 PM <tonikitoo> (For me to look at)
6:24 PM <tonikitoo> Hum, thought of this too. The hardest part of testing this on mac is that overlay scrollbars only show up when actually scrolling.
6:25 PM <tonikitoo> A always on mode for it could help.
6:31 PM <tonikitoo> smfr: So, to wrap up: a always-on mode for overlay scrollbars + a mismatch ref test would make you happy with it?
6:32 PM <tonikitoo> IIRC webkit/gtk+ has its overlay scrollbars always on.
6:34 PM <smfr> tonikitoo: yes!
6:35 PM <smfr> tonikitoo: probably two separate patches
6:35 PM <smfr> tonikitoo: also note that overlay scrollbars have three modes: hidden, narrow, wide
6:37 PM <tonikitoo> Sounds good. If my understanding is correct, 'wide' happens when scrolls (say with mouse wheel) gets triggered with mouse is hovering the scrollbar, right?
6:37 PM <tonikitoo> Where 'narrow' is the thumb-only mode.
6:38 PM <tonikitoo> smfr: does it sounds correct?
6:38 PM <smfr> right
6:38 PM <smfr> ideally we could call internals to set the bars in either mode
6:38 PM <tonikitoo> K. Will give it a try. Thanks!