A new test 'sampler-struct-function-arg' fails with ToT WebGL.

Change-Id: Ie62208364ceacd4b980cb16f5de31cc4b5c62fa1
Reviewed-on: https://chromium-review.googlesource.com/243594Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>