[fetch] Feed a Response to existing APIs (#49)

If you manage all network activity yourself you still need a way to inject the results into existing APIs that consume them. There's two approaches here that I know of:

    <img>.srcObject = responseInstance
    <img>.src = convertResponseToURL(responseInstance)

The first is more elegant, the second invokes Fetch twice (but the `convertResponseToURL()` URL should be a way shorter trip). If we go with the second, which scales better due to the many APIs in existence, we need to avoid the flaws from blob URLs and make sure the URL can be used only once and consumes the underlying stream (you cannot use `responseInstance` again, if you wanted to do that you'd have to clone it first).

---
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fetch/issues/49