Add vasilyt@chromium.org to gpu/OWNERS

Change-Id: Id0dd733f9f3022a6b0b75b92d4db97d9417ade84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2595690Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Jonathan Backer <backer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837698}

gpu/OWNERS

 backer@chromium.org
 kbr@chromium.org
 khushalsagar@chromium.org
+vasilyt@chromium.org
 vmiura@chromium.org
 zmo@chromium.org
 sunnyps@chromium.org