bbaa91e912
Without this there is no way to get source maps on the else if in e.g.
```
if (core.StateError.is(e$)) {
core.print("StateError");
} else if (core.ArgumentError.is(e$)) {
let e = e$;
{
core.print(dart.str`ArgumentError: ${e}`);
}
}
```
Bug:
Change-Id: I0203fe7f1e0c14c677e16d61e7649624b72d41cd
Reviewed-on: https://dart-review.googlesource.com/23673
Reviewed-by: Vijay Menon <vsm@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>