In Bug 234966 and Bug 238239 changes are being made to the validation for the WEBGL_multi_draw extension. The conformance test conformance/extensions/webgl-multi-draw.html should be added to the EWS bots to prevent any future regressions in this area. Perhaps this will come along with the upgrade to the 1.0.x and 2.0.y versions of the conformance suite?
This is a dupe of bug 220753. EWS doesn't run flaky tests, because they do not provide any signal as to whether a patch is good to land. LayoutTests/TestExpectations:3621:webkit.org/b/220753 webgl/conformance/extensions/webgl-multi-draw.html [ Pass Failure Slow ] *** This bug has been marked as a duplicate of bug 220753 ***