We had two separate minor bugs. 1) missing a flush of the image data
and 2) missing an initial barrier to set the image to TRANSFER_DST.

Bug: angleproject:2652
Bug: angleproject:2653
Change-Id: I485aafc5c9055b5efb101cb2bc3ebab0588d2639
Reviewed-on: https://chromium-review.googlesource.com/1249564
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>