X11Window: handle key presses and releases BUG=angleproject:892 Change-Id: I66690ba49789faa672f6ed58e9eb8a2482eb4f6d Reviewed-on: https://chromium-review.googlesource.com/283472 Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Corentin Wallez <cwallez@chromium.org>