Loading an SVG resource and not waiting for completion causes the test to occasionally flake as IMAGE failure. http://test-results.appspot.com/dashboards/flakiness_dashboard.html#showExpectations=true&showLargeExpectations=true&useWebKitCanary=true&tests=fast%2Fblockflow%2Fblock-level-images.html
Rebaselining, seems fine now.