Re: [whatwg/streams] Support transferable streams (postMessage) (#1053)

@ricea commented on this pull request.



> +
+<div algorithm>
+ <dfn abstract-op lt="SetUpCrossRealmTransformReadable">SetUpCrossRealmTransformReadable(|stream|,
+ |port|)</dfn> performs the following steps:
+
+ 1. Perform ! [$InitializeReadableStream$](|stream|).
+ 1. Let |controller| be a [=new=] {{ReadableStreamDefaultController}}.
+ 1. Let |backpressurePromise| be [=a new promise=].
+ 1. Add a handler for |port|'s {{MessagePort/message}} event with the following steps:
+  1. Let |data| be the data of the message.
+  1. If ! [$Type$](|data|) is not Object, return.
+  1. Let |type| be ? [$Get$](|data|, `"type"`).
+  1. Let |value| be ? [$Get$](|data|, `"value"`).
+  1. If ! [$Type$](|type|) is not String, return.
+  1. If |type| is `"chunk"`,
+   1. If ! [$ReadableStreamDefaultControllerCanCloseOrEnqueue$](|controller|) is true,

Yes, because we don't want to reset the backpressure otherwise. Although now you mention it, maybe it doesn't make any actual difference.

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