This micro-benchmark can be used to measure the performance impact
of changing the Pipeline cache. For instance, we can check if changing
the size of the hash key affects performance significantly.

Also updates the build files so angle_perftests can see vulkan.h, and
makes the Vulkan headers an explicit source set.

This test currently shows that a lot of time is spent in PMurmurHash,
with some time also spent in memcmp.

Bug: angleproject:2163
Change-Id: Ie8bb3e31d58590f373d28cbbb59f7e372b80cc29
Reviewed-on: https://chromium-review.googlesource.com/884882
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>