Re: [streams] Add readableAmount getter to ReadableByteStream (#279)

`readableAmount getter` was proposed for users of hypothetical underlying sources which can tell how many bytes can be read synchronously to pass a single contiguous buffer of sufficient enough size to `readInto()` call while keeping it able to consume only part of the synchronously readable data not to replenish back pressure too much.

But when I revisited the issue, I think that it doesn't make much sense.
- If the total size to read into a single contiguous buffer is known, they can just allocate a buffer of the size and repeat invoking `readInto()` until it's filled.
- If the total size is unknown, we may still need to repeat `readInto()` calls if parts of data arrive little by little.

If reading into a single contiguous buffer doesn't really matter, we can just read into some small buffer and process bytes in it repeatedly. It just works.

`readableAmount getter` just reduces the number of `readInto()` call. That's not big benefit. Closing for now. Can be opened if necessary.

---
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/streams/pull/279#issuecomment-81457193