1708272 - Improve performance of JSStructuredCloneReader::read

Status: NEW

(Core :: JavaScript Engine, task, P3)

Description

[Iain Ireland [:iain]]

In bug 1680860, the retrieval of large objects from indexedDB causes jank. We spend a long time adding properties to the object (js::DefineDataProperty / NativeObject::addPropertyInternal`).

As a follow-up to the reshape work, we should be able to optimize this code better. (Jan in chat: "we will be able to fill the property map directly and can then allocate the shape, bypassing a lot of the generic define code")