Add hook_commerce_product_add_extra_fields_alter or similar to replace hook_field_extra_fields_alter functionality

I'm trying to get a new 'commerce_product' entity property (not field) I've added to show up on a product reference node. To do this, I've added the property with hook_field_extra_fields_alter() and hook_entity_property_info_alter(). However, it's impossible to get this new property to work with the 'product_reference' module's pattern for field injection.

The 'product_reference' module calls commerce_product_field_extra_fields() directly instead of field_info_extra_fields().

        // Attach extra fields from products that may be visible on the bundle.
        // We have to call commerce_product_field_extra_fields() directly
        // instead of using field_info_extra_fields() because of the order in
        // which these items are rebuilt in the cache for use by "Manage
        // display" tabs. Otherwise these extra fields will not appear.
        $product_fields = commerce_product_field_extra_fields();

In this code: commerce_product_reference_field_extra_fields()

Because it calls commerce_product_field_extra_fields() directly, my hook_field_extra_fields_alter() is never called to add the new property as an extra field. I understand the reason why you're calling commerce_product_field_extra_fields() directly is because it's called inside of a hook_field_extra_fields() function and would recurse to infinity if you called field_info_extra_fields().

I propose a work around of exposing a hook_commerce_product_add_extra_fields_alter() in commerce_product. Then drupal_alter('commerce_product_add_extra_fields', $extra); can be called in commerce_product_field_extra_fields(). This will allow a custom module to implement this hook and expose their extra fields.

If you have another solution, please let me know.

Patch to follow.