When used in an iframe in a different domain (or port) Chrome triggers "multiple files" warning/block

This also applies to other Chrome-based browsers, like Edge-dev.

Basically if FileSaver.js is used (a simple example like that shown in https://github.com/eligrey/FileSaver.js#saving-text will do it) inside an iframe from a different domain or port, it will cause Chrome to show the "download multiple files" warning.


I couldn't create a jsfiddle as both HTML documents would be on the same domain and not trigger the issue, but it can be easily replicated downloading this zip file:
- [mutiple-downloads-issue-replication.zip](https://github.com/eligrey/FileSaver.js/files/3998570/mutiple-downloads-issue-replication.zip)

Inside there is basically these two HTML files, FileSaver.js, and a README with simple instructions to launch 2 Python localhost servers.

## index.html (http://localhost:8080/index.html)

```html

Test

```

## iframe/index.html (http://localhost:8090/index.html)

```html

Click me


document.getElementById("downloadLink").addEventListener("click", function foo(e) {
var blob = new Blob(["Hello, world!"], {type: "text/plain;charset=utf-8"});
saveAs(blob, "hello world.py");
});

```