but if you put this line in the non-minified file just like you originally did via .prefix files then browser thinks that it needs to map the non-minified file.

on the other hand if you just inject this line into the minified file after minification and map generation then the mapping line offsets are wrong and stepping through the code is broken. (try debugging with the build of angular from your branch and you'll see that stepping through the code will result in weirdness).

I guess the solution then is to append 

```
/*
//@ sourceMappingURL=...
*/
```

instead of just 

```
//@ sourceMappingURL=...
```

to the file.