The checks for VertexAttribPointer were already implemented in a
previous patch, so we only add the checks for DrawElements.

BUG=angleproject:1523
BUG=chromium:668223

Change-Id: I5da55f9a7e7479627099c7f77618353a63b75a8e
Reviewed-on: https://chromium-review.googlesource.com/434958
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>