GitLab

Exo could not handle some cases of popup placement, particularly when
the new window would be too large to fit on screen.

This CL reworks the implementation in some ways:
 - We break the placement problem down into two 1D problems, which
   minimises code duplication.
 - We respect the transformation order specified in the wayland spec,
   i.e. flip > slide > resize.
 - We maximize the visibility of the popup subject to the above, so
   when no valid transformations result in an unconstrained window, we
   choose the transformations that make the popup most visible.
 - We handle the case of resize, where previously only the top-left
   corner of the popup could be chosen.
 - We properly send the configuration callback, to inform the popup
   surface of its actual placement.

Bug: 942859
Change-Id: I892678492047ac2849afa84b1004731b7decab92
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1588058
Commit-Queue: Nic Hollingum <hollingum@google.com>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659400}