It was mostly being included for gl::error or the debug.h include.

BUG=angle:733

Change-Id: If40d511c5422ac9265fbd809f647a91bcc802d41
Reviewed-on: https://chromium-review.googlesource.com/230551Reviewed-by: Brandon Jones <bajones@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>