It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat.

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

The code looks good.
As for naming, do we use up/down in Flutter at all? I thought we've been sticking to top/bottom. Also if we use up/down, then should we name the resize-nw as UpLeft or UpperLeft?

Do we support the resize-nw cursor right now?

The top/bottom usages I've seen refer to regions, whereas this refers to directionality. Is there a case where we use top/bottom for directionality?

Do we support the resize-nw cursor right now?

Not yet, but only because of low priority, the same as these two cursors.

The top/bottom usages I've seen refer to regions, whereas this refers to directionality. Is there a case where we use top/bottom for directionality?

You're right. So what name do you think they would be (as well as diagnal cursors such as resize-nwse)? Just want to plan everything ahead.

Do we support the resize-nw cursor right now?

Not yet, but only because of low priority, the same as these two cursors.

FYI, diagonal resize aren't system cursors on macOS, so if we want to support them it'll require custom embedding support.

Maybe horizontalDoubleArrow and verticalDoubleArrow would allow for expansion room (if we decide to do the custom embedder work)?

There are lots of cursors that aren't shared between platforms. The plan is to make them fall back to other cursors, such as the basic cursor, so that the superset of all cursors is available to the framework by all platforms, although some don't work in the best way. In other words, having diagnal resize cursors in the framework doesn't mean they will be supported by all platforms, but only that they will be supported by some platforms.