Starts/resets the high resolution profiling timer. Subsequent calls to
debugprofilestop() will return the current value of the timer.
Note that debugprofilestart() is more of a global reset than a "start". It is not necessary to call it, ever. In fact, it is probably a much better idea to simply do 2 calls to stop() and calculate the difference, since calling start() will interrupt timing measurements done by other addons.
See also Debugging and Profiling functions.