[streams] readBatch() or getSyncReader() (#327)

Sub issue for #320.

It's still under discussion whether we should take care of the promises overhead. It's discussed at #320.

As @wanderview analyzed in https://github.com/whatwg/streams/issues/320#issuecomment-91692373, there should not any big performance difference between them.

But as I questioned in https://github.com/whatwg/streams/issues/320#issuecomment-91606599, `readBatch()` and `getSyncReader()` have different power for recognition of the consumer's signal. This comment by me elaborates the first bullet point in the comment by Ben.

Domenic +1-ed readAllAvailable() at https://github.com/whatwg/streams/issues/320#issuecomment-91608679 to avoid confusion.

So, currently I see three approaches:

1. provide readAllAvailable() on async reader
1. provide readBatch(N) on async reader
1. add getSyncReader()

---
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/streams/issues/327