The macros don't need to disambiguate between GL/EGL. Also make
helpers to deal with ErrorOrResult.

BUG=angleproject:1310
BUG=angleproject:1327

Change-Id: I8041c4b17a859fe1f236bca3ad266453d67a8fd4
Reviewed-on: https://chromium-review.googlesource.com/335826Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>