The following Javascript snippet works in Chrome by using the new 'download' attribute of links and simulating a click.
function downloadWithName(uri, name) {
var link = document.createElement("a");
link.download = name;
link.href = uri;
link.click();
}
And the following example shows it's use:
downloadWithName("data:,Hello%2C%20World!", "helloWorld.txt")