The mAcquireImageSemaphore is for achieving the maximum overlap between
display engine and rendering engine. We should only need to block when
we write to the swapchain image. Work that doesn't touch the visible
buffer can proceed.

Bug: b/157916459
Change-Id: Ic9a9a1f2a7648ef7f50f99578a0f0d674ae5e66c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2223826
Commit-Queue: Charlie Lao <cclao@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>