[streams] Some tests behaving differently (#390)

I have a replica of the spec tests ported to WebKit to run them against the reference implementation. I realized that after your changes, there were some issues with the moment closed is fulfilled in reference to the last read. And in some cases it seems to be inconsistent.

For example, in the RS tee tests, at "ReadableStream teeing: should be able to read one branch to the end without affecting the other" we were getting closed before the last read, which is no longer true with the reference implementation.

For the templated tests, in the case of Errored, "ReadableStream (errored via call in start)" behaves different from "ReadableStream (errored via returning a rejected promise in start)" regarding "getReader() should return a reader that acts errored".

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/streams/issues/390