Have Vulkan advertise that compressed textures are currently unsupported

This allows the ProxyTest to run on the Vulkan backend.

Change-Id: I89a3212bdc2d4a1ceb0c27d0ff60f558d7b12647
Reviewed-on: https://skia-review.googlesource.com/7880
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
2 files changed