We were passing the arguments from the gl::Buffer stub to the
implementation class, which was breaking the call.

Also clean up a few comments.

BUG=angle:709

Change-Id: Ib92a36d1c52d60d8929f567d0daf54e9d6a2d127
Reviewed-on: https://chromium-review.googlesource.com/210641Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>