Use sourcemaps for leaking classes in heap snapshots

[nolanlawson]

Rather than say that an object named Zx is leaking, it would be great to show the original name. Now that #25 proves we can have sourcemaps, it seems like it should be possible to extract sourcemaps for heap snapshot class names. (I mean, the DevTools seem to be able to point a retainer chain back to the leaking line of code, so why not?)

I don't know if this is actually possible, though.