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Context: Wayland Protocol needed to be extended to make it possible to
properly support full Chromium's tab dragging experience. Further
details in the Design document [1].

This patch contains the first round of Wayland Ozone backend (client
side) changes needed to leverage the extended-drag protocol extension to
implement the remaining tab/window dragging missing features, whereas
the main one is the ability to set a toplevel shell surface (browser
window) as the "dragged surface", making it to be anchored to the
pointer cursor as it's dragged around, as well as being smoothly
droppable anywhere in the workspace, which is not possible with the
standard Wayland DND protocol.

[1] https://docs.google.com/document/d/1s6OwTi_WC-pS21WLGQYI39yw2m42ZlVolUXBclljXB4/edit?usp=sharing

R=msisov@chromium.org

Bug: 896640, 1099418
Change-Id: I8a19670fd4ad64d49a9aa202548c22065870dd90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2401319
Commit-Queue: Nick Yamane <nickdiego@igalia.com>
Reviewed-by: Maksim Sisov (GMT+2) <msisov@igalia.com>
Reviewed-by: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#823987}