a-cubemap as asset in component

Description:

• A-Frame Version: 0.9.2 (Date 2019-05-06, Commit #f57a1fa)
• Platform / Device: all
• Reproducible Code Snippet or URL:

When defining a schema type as asset and providing the id of an a-cubemap the asset in the component is null.

Expected:
Expected a node that I could use .srcs and get the cubemap images.

What I've figured out so far.

Updating the assetParse function to include A-CUBEMAP would pass the el through as expected.
https://github.com/aframevr/aframe/blob/f863f01206a25951eb39b389ae7031885153143a/src/core/propertyTypes.js#L90

if (value.charAt(0) === '#') {
    el = document.getElementById(value.substring(1));
    if (el) {
      // Pass through media elements. If we have the elements, we don't have to call
      // three.js loaders which would re-request the assets.
      if (el.tagName === 'CANVAS' || el.tagName === 'VIDEO' || el.tagName === 'IMG' || el.tagName === 'A-CUBEMAP') {
        return el;
      }
      return el.getAttribute('src');
    }
    warn('"' + value + '" asset not found.');
    return;
  }

If there is no specific reason why not to do this, then I will fork and do a pr

Start in src/core/propertyTypes.js at the assetParse function and review how an asset reference is resolved for an a-cubemap element. Reproduce the reported schema case and verify that resolving its id returns the a-cubemap node, including its usable srcs property.