The dEQP varying struct linkage tests were triggering
asserts when we tried to query component info of struct types.

BUG=angle:580

Change-Id: I61e33573c5577a327c58fec7a07ae7718690ac42
Reviewed-on: https://chromium-review.googlesource.com/189194Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>