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This change simplified the semaphore logic in VulkanSwapChain by reusing
VkSemaphores. It also improved performance on Linux workstation
slightly, but it could improve more if vkCreateSemaphore() is heavy for
some other platforms.

Bug: 1004772
Change-Id: Ifa5c5255627b4824b946f62d6edfa8d3f0c2ecb5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2331000
Commit-Queue: Peng Huang <penghuang@chromium.org>
Reviewed-by: Michael Spang <spang@chromium.org>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Auto-Submit: Peng Huang <penghuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795368}