initial support of text-input-unstable protocol

This CL introduces the support of text-input-unstable protocol
defined in wayland-protocols repository.

This CL will be the first one for a series of CLs for supporting
this protocol and lacks some parts surrounding text.

BUG=826614
TEST=manually, exo_unittests

Change-Id: I4f4e335ed26c51beea9f25479acc63e11f09f777
Reviewed-on: https://chromium-review.googlesource.com/1132332
Commit-Queue: Jun Mukai <mukai@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577022}
11 files changed