SkiaRenderer: Call Begin{Read,Write}Access just before and after skia flush()

This CL a preparing CL for avoiding extra command buffer submission.
Next we will gather semaphores from shared image and create end read access
semaphores before calling skia flush(). And the skia flush() will submit
command buffer which will wait begin read read semaphores before execution,
and signal end read access semaphores when the GPU execution is done.

Change-Id: I32515417316f1b9b55da3b56bedc4828dde0ad3a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1557789
Commit-Queue: Peng Huang <penghuang@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Eric Karl <ericrk@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#651513}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: bc77533cdd83301adf6b876657f2bc596e00847b
1 file changed