Another try at finding the new markVisible() crasher without de-optimizing it too badly.  Sprinkle it with asserts for the sanity checks we've started to skip, see which one (ones?) fires.
Another try at finding the new markVisible() crasher without de-optimizing it too badly.  Sprinkle it with asserts for the sanity checks we've started to skip, see which one (ones?) fires.

gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm