Now works when run in a sequence. Also saves RGB images to avoid
issues with the alpha being inconsistent and also flips images
vertically to fix the rendering.

Bug: angleproject:4615
Change-Id: I8d3b38c5d914e0ca2227320ac42a0e28acd12c4d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2187971
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>