We were missing the data definition for the standard validation layer.
This file was missing from the isolate, and the entire layer system
was not working.

Found this as a side-effect of working on depth stencil support.

Also fixes a missing definition in the white_box_tests BUILD.gn.

Also temporarily disables the ClearTest support for Vulkan because of
an implementation bug on AMD. Unfortunately because of the failure
mode it didn't work to just skip the test in the preamble.

Bug: angleproject:2357
Change-Id: I4d06c54191b09e09a4ba68c24613db6f148b17e3
Reviewed-on: https://chromium-review.googlesource.com/956759
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>