This patch fixes titlebutton rendering in Chromium. The headerbar used by Breeze is the same size when a window is maximized, but Chromium uses a smaller headerbar for its tabstrip background when the browser is maximized. When buttons won't fit, Chromium downsizes buttons. This was happening with Breeze titlebuttons since it used 6px of padding on the top and bottom of the buttons, so the buttons appeared taller than they actually were. This patch changes the top and bottom padding to 1px. In native GTK apps, there's no change in appearance.
Thanks for the comment. I will leave this to the dev team. My vote was as support for this visual change as I am part of the Visual Design Group. The dev team will also review and push the revision upstream if they determine that it is a sensible change.