image requests that used to be queued can't be aborted

[ansis]

Image requests that are queued return a Cancelable object that only cancels the request if the request is still queued. Once the request has been unqueued it is not possible to abort the network request. Calling cancel at that point will do nothing.

mapbox-gl-js/src/util/ajax.js

Line 186 in 16a0c1d

return { cancel() { queued.cancelled = true; } };

@mourner I don't think this should block the beta because it is already in the previous version. should it block the final release?

mapbox-gl-js version: v0.50 and master

browser: all

Steps to Trigger Behavior

1. open http://localhost:9966/debug/satellite.html#7.85/58.009/-113.643 in large viewport to queue up image requests
2. wait a bit so that some requests complete and queue requests start
3. zoom quickly to abort requests

Link to Demonstration

http://localhost:9966/debug/satellite.html#7.85/58.009/-113.643

Expected Behavior

Requests for previously queued images abort.

Actual Behavior

Requests for previously queued images do not abort.

[mourner]

It's not critical but may affect performance, so I'd cherry-pick the fix into beta if there's time. Submitted a potential fix in #7655.