The user agent quirk for Slack does not seem to be necessary anymore. I am able to use Slack without difficulty using our default user agent. The quirk is not causing any harm, so there's no need to backport this to stable just in case I've messed up, but we should not retain quirks in trunk when they are no longer necessary.
Created attachment 309517 [details] Patch
Comment on attachment 309517 [details] Patch Attachment 309517 [details] did not pass ios-sim-ews (ios-simulator-wk2): Output: http://webkit-queues.webkit.org/results/3706904 New failing tests: imported/w3c/web-platform-tests/streams/readable-byte-streams/general.html
Created attachment 309525 [details] Archive of layout-test-results from ews123 for ios-simulator-wk2 The attached test failures were seen while running run-webkit-tests on the ios-sim-ews. Bot: ews123 Port: ios-simulator-wk2 Platform: Mac OS X 10.11.6
Comment on attachment 309517 [details] Patch Don't we have a unit tests checking this quirk too?
Yup, good catch
Committed r216585: <http://trac.webkit.org/changeset/216585>