Try passing the argument "-1":

run-webkit-tests --ios-simulator -1

Great thanks for the hint, I think this --dump-render-tree could be useful indeed to check WK1.

However, in the particular scrolling tests I'm considering, I'm relying a lot on testRunner.runUIScript to execute basic gestures or emulate the find UI and most of these APIs are not implemented (easily implementable?) in Tools/DumpRenderTree/ios/UIScriptControllerIOS.mm

-- 
Frédéric Wang - frederic-wang.fr