Bug 1669567 - Increase the default tile size used for scrollbars. r=jnicol
Bug 1669567 - Increase the default tile size used for scrollbars. r=jnicol

Most platforms have scrollbars > 16 pixels in width. This typically
reduces the number of native layers allocated on most platforms for
scrollbars. This is quite important as the fixed overhead of each
native layer is relatively high on DC and CA.

Differential Revision: https://phabricator.services.mozilla.com/D92871

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/18fb8d11fd2d8b85ff361c3323729a47ee4577ff

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender