The resource manager factory methods will use ClearView or zero-filled
buffers to set initial data. It assumes there are no 3D depth/stencil
textures. This will lead to some wasteful re-creation of RTVs in some
cases.

This is a temporary measure until we can implement more efficient
lazy resource init strategies.

BUG=angleproject:1635

Change-Id: I590e76587d3d96a359beedb79e21d24930e5f2e0
Reviewed-on: https://chromium-review.googlesource.com/503254Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>