PaymentInstruments .set() and icons

[marcoscaceres]

The .set() algorithm has a whole bunch prose about icon processing. However, I don't think that is the right place to do any of the processing specified there.

We should have a dedicated section for displaying icons, but storage of a payment instrument should just store the instrument, and not do any icon processing.

[rsolomakhin]

When should icon processing happen?

[marcoscaceres]

At display time, I think. We should do some light validation checks here. Working on a proposal.

[rsolomakhin]

We would probably want to have some kind of caching to reduce paymentRequest.show() latency due to loading the icons.

[marcoscaceres]

Potentially, yeah... that's a tricky one. We need to check what the Notifications API does.

[rsolomakhin]

Sounds good. I'm all for re-using existing paradigms, if Notification API has it all figured out already.

[agektmr]

Let me cross reference to a related issue here.
cc: @kenchris