TestWebKitAPI.WebKit2CustomProtocolsTest.CloseDuringCustomProtocolLoad seems flaky. In https://ews-build.webkit-uat.org/#/builders/19/builds/2524, the test Crashed in run-api-tests step. However, in the immediately next retry step (re-run-api-tests), it passed. Similarly, in https://ews-build.webkit-uat.org/#/builders/19/builds/2519, the test Passed in run-api-tests step. However, in the immediately next retry step (re-run-api-tests), it Crashed.
This test was added long back in https://trac.webkit.org/changeset/211915/webkit
Created attachment 365961 [details] Crash log
<rdar://problem/50509873>
This doesn't seem to be happening any more.