Assert no GL errors at the end of image tests Bug: angleproject:42265697 Change-Id: Iac9241d0fbe384b10fc0b0f6b2f764efca674ac3 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6032805 Reviewed-by: Yuxin Hu <yuxinhu@google.com> Commit-Queue: Yuxin Hu <yuxinhu@google.com> Auto-Submit: Shahbaz Youssefi <syoussefi@chromium.org>