Need to reuse web app manifest ImageResource better.

[rsolomakhin]

Feedback on Payment Handler TAG review by @dbaron:

ImageObject is similar to web app manifest's ImageResource, but it: (1) doesn't have the two last properties, (2) has a differing type for type (DOMString vs. USVString).

IMHO, we should reuse web app manifest's ImageResource verbatim to ease both spec authoring and implementation.

[domenic]

This is a dupe of #238, where I noted that I think it's actually not a good idea.

[rsolomakhin]

@dbaron: Would you agree with @domenic's logic in #238?

[kenchris]

I wouldn't. Platform and purpose are hints, so I don't see why they don't apply, for the same reason they exist in the web app manifest

[ianbjacobs]

SInce this is a dupe of #238 I am going to close this issue and ping David Baron on that thread.