I've introduced a bad bug in 10569.0 for vm builds and it get fixed in 10570.0.  With that bug, chrome os will always show a blackscreen when running that image inside vm. But tests are happy and both CQ and canary build didn't report any issue even the actual screen won't show anything. We should detect blackscreen in tests. We can get screen dump from vnc clients for vm or just use screenshot.py for real devices to check if there is something showed on screen.