Multiple alerts do not work inside loop

```
for (var i = 0; i < 3; i++) { alert(i); }
```
will only show 1 alert.

Reason: Due to `alert`, the time taken inside loop is too long, enough to be detected as an infinite loop and hence loop breaks after 1st alert.

https://twitter.com/vikrant_negi/status/846270825800126464

Reproduce the provided for-loop in Web Maker and trace the execution path that detects infinite loops; the issue names no file or test. Done means the exact snippet produces three alerts without being stopped after the first, with a regression check for this behavior.

Written by the indexing model from the issue text.