As a first step in experimenting with Vulkan in Chromium, this CL adds
GN rules to build and link with Vulkan under the GN variable
"enable_vulkan".

Currently we require users to have the Vulkan SDK installed, so the
changes will not link unless a user has properly installed the SDK.

R=piman@chromium.org
BUG=582558
CQ_INCLUDE_TRYBOTS=tryserver.chromium.win:win_optional_gpu_tests_rel;tryserver.chromium.mac:mac_optional_gpu_tests_rel

Review URL: https://codereview.chromium.org/1726303002

Cr-Commit-Position: refs/heads/master@{#380210}