Also adds the build files for the Vulkan layers.

The layers are enabled by default for the tests.

BUG=angleproject:1319

Change-Id: I0b442b36312a1299a932922e1c4e39f00801de49
Reviewed-on: https://chromium-review.googlesource.com/367751
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>