With our added padding to some structures, using only 'out' in the
generated HLSL can cause warnings because not all of the structure members
are initialized.

BUG=angle:286

Change-Id: I866960883de487f19883fb2bc086c02703ea6271
Reviewed-on: https://chromium-review.googlesource.com/201364Reviewed-by: Nicolas Capens <nicolascapens@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>