EXO: Added FullscreenShellSurface

Created FullscreenShellSurface class, similar to ShellSurface but without
any ash dependencies, to be used with fullscreen wayland protocol
to allow EXO use on other platforms.

Added unit test for FullscreenShellSurface for cast.

Bug: 896710
Test: Compiled on ChromeOS
Change-Id: I542c9b0729b847f4cde2fa67d727143e18f4a2a5
Reviewed-on: https://chromium-review.googlesource.com/c/1298172
Commit-Queue: Shawn Gallea <sagallea@google.com>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607237}
6 files changed