Flash can't run natively "on webkit." Flash file contains bytecode, which has to be either fully interpreted or JIT-ed. It has to be done on mobiles too. The interpreter or JIT-er has to be native. Writing native JIT-ers is hard, to have a native interpreter you can write it in C and recompile it for every platform but it will be significantly slower. In short, it's not easy to make the Flash fast on a new CPU. And no, Webkit is not a CPU.