[wayland] Support ext-drag protocol extension
In order to fully support Chrome's tab dragging features under Wayland, Chromium team developed a new protocol extension, which has been proposed upstream at wayland-protocols/#46. Field trials for Chromium/Wayland should start soon, and it'll basically fall back to X11 backend in case the extensions required are not supported by the Wayland compositor in place.
For reference, a zcr_
-prefix variant of it was implemented in Exosphere, ChromeOS' Wayland Compositor, and a bunch of possibly relevant info can be found on this design doc. Also a few demos of it in action can be seen here.
Edited by Nick Yamane