Web reality: Load/error events for <link> not firing on rel="icon"

[andreubotella]

While trying to write some tests for #3483, I noticed that per the spec <link rel="icon"> should fire a load or error event, but none of the major browsers implement this, even when the icon is showing in the browser chrome.

By the spec, the default process the linked resource algorithm fires the load and error events, but that algorithm only runs if all of these conditions hold:

• the <link> element represents an external resource link
• the link type defines an appropriate time to fetch and process the linked resource (presumably rel="icon"'s "should be used by the user agent when representing the page in the user interface" counts here)
• the link type doesn't override the fetch and process the linked resource algorithm (since it calls process the linked resource)
• the link type doesn't override the process the linked resource algorithm

The only currently defined link type that fulfills all of those conditions is rel="icon", so it might be best to make the default process the linked resource algorithm a noop, though I'd be fine with defining custom process the linked resource steps for rel="icon". Other link types that fire the load and error events, such as rel="stylesheet" and rel="prefetch", do so in their overriden "process the linked resource" algorithms, and so aren't affected.

See also web-platform-tests/wpt#21352, which points out the lack of tests.

[domenic]

Great find.

Upon reflection, I think making the default steps a no-op is probably best. Most links will need custom handling, and so the default steps don't buy us much.

/cc @domfarolino