Web updates

Streams d5f92d9f1730

Reject pending reads when releasing a reader Currently, reader.releaseLock() throws an error if there are still pending read requests. However, in #1103 we realized that it would be more useful if we allowed releasing a reader while there are still pending reads, which would reject those reads instead. The user can then acquire a new reader to receive those chunks. For readable byte streams, we also discard pull-into descriptors corresponding to (now rejected) read-into requests. However, we must retain the first pull-into descriptor, since the underlying byte source may still be using it through controller.byobRequest. Instead, we mark this descriptor as "detached", such that when we invalidate this BYOB request (as a result of controller.enqueue() or byobRequest.respond()), the bytes from this descriptor are pushed into the stream's queue and used to fulfill read requests from a future reader. This also allows expressing pipeTo()'s behavior more accurately. Currently, it "cheats" by calling ReadableStreamReaderGenericRelease directly without checking if [[readRequests]] is empty. With the proposed changes, we can safely release the reader when the pipe finishes (even if there's a pending read), and be sure that any unread chunks can be read by a future reader or pipe.

Mattias Buelens