Need to include gtest before X11 to avoid defines conflict

BUG=angleproject:2348

Change-Id: If758c53fb5ef010506f13165186110f00c099e07
Reviewed-on: https://chromium-review.googlesource.com/919687Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>