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GL uses triple buffering, but Vk was set to use double in most cases.
Bump Vk to triple buffering for now.

Change-Id: I8e68106b5f0306eb6867382d58d1195341d62a07
Reviewed-on: https://chromium-review.googlesource.com/c/1388223Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Commit-Queue: Eric Karl <ericrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619978}