Inintialize all D3D11 texture allocations with dummy values in debug.

BUG=angleproject:2107
BUG=angleproject:1635

Change-Id: Ibcc6cc30480b32430563143f35f38dda16fdb83c
Reviewed-on: https://chromium-review.googlesource.com/678477
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>