Remove interoperability between TypedArrays and DataView instances

[leobalter]

Apply this change to prevent this - probably unwanted - interoperability.

This change help optimizing implementations.

[anba]

Does anyone know the history behind the previous design? The change notes for rev19 only say:

Changed branding for DataView to make them more polymorphic with Typed Arrays WRT buffer access and ArrayBuffer.isView

[leobalter]

From what I saw on the specs, TypedArray and Dataview instance methods are very optimized to work for their respective constructors. I might be wrong, but this interoperability is not necessary and might avoid further optimization.

It would be valuable to have feedback on @anba's question, maybe there's a missing piece I haven't found yet.

[littledan]

@allenwb What do you think?

[allenwb]

I'll take a closer look in a bit. A good starting place for understanding the motivation is to look at the change markup for Rev19 and see the before and after.

[bterlson]

ping @allenwb? :)

[allenwb]

OK, I verified that this is indeed a bug and the proposed fix looks exactly right.

[leobalter]

Thank you, @allenwb!

[littledan]

I like this change. Suggestion: maybe completely disjoint internal slot names to make the distinction even more clear.

[allenwb]

the common [[ViewedArrayBuffer]] is used to make ArrayBuffer.isView work ... or anything else that wants to work with any view over an ArrayBuffer. For example, output primitives might accept either an Typed Array or a DataView.

[leobalter]

I left the Assert steps for [[ViewedArrayBuffer]] for a historical reason, but they're not really necessary as probably won't cause any trouble.

I can remove them if necessary.

[bterlson]

The asserts are fine I think. Let's leave them!