Bug 188243

For example, we end up with N*file size memory use here:

```
let files = [];
for (let i = 0; i < 100; ++i)
    files.push("foo.js");

async function load(url) {
    let fetchResponse = await fetch(new Request(url));
    let text = await fetchResponse.text();
    return text;
}

async function loadEverything() {
    let text = [];
    for (let url of files)
        text.push(await load(url));
    return text;
}
```

This is especially bad when "foo.js" is a large file.