df415528 implemented a feature where
images are not created with the storage flag until needed.  This is a
necessary optimization.

There were a few misuses of the BufferHelper::onRead/Write helpers that
set up the appropriate barriers that this change fixes.

Bug: angleproject:3816
Change-Id: I7e62d98b7325f938152a1972f4ebee083ed319c2
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1924989
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Xinyi He <xinyi.he@arm.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Sunny Sun <sunny.sun@arm.com>