We rely on TSymbol::name() to generate names also for nameless
parameters. Fix asserts to reflect this.

BUG=chromium:823041
TEST=angle_unittests

Change-Id: Ie9b8253a150e79965bf85d8a7f36643ada6c54cc
Reviewed-on: https://chromium-review.googlesource.com/968242Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>