Bug: angleproject:2393

Moving to HEAD of LVL master on afternoon of 3/6/18.
Made some updates to BUILD.gn to add args to spirv tools
external_revision_generator.py script.
Re-enable ANGLE Vulkan build.

Change-Id: I1705d7a2acae578bab9bbd8bb93176107e0e21dc
Reviewed-on: https://chromium-review.googlesource.com/952547Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>