EXO: Fullscreen protocol server implementation

An incomplete implementation of the fullscreen shell protocol,
separated from server.cc to allow selective compilation for
different platforms that support EXO. The rest of the protocols within
server.cc will be refactored in future CLs.

Bug: 896710
Test: Compiled on ChromeOS, works with fullscreen client
Change-Id: Idda3b73c97c72e5efd16dfe1f7c79831587c8066
Reviewed-on: https://chromium-review.googlesource.com/c/1299838
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@{#607369}
5 files changed