Query builder - Allow spatial restriction based on specified layer

Currently the query builder in the HTML5 viewer only has 2 options for restricting the results of a query - none or current extent.

We would like be able to further limit the query to a specific layer or features within another layer.

For example we might want to query on airport_type="heliport" but restict it to results from the fire_regions table where region_name = "northwest"