| These tests exercise different ways to fetch a resource (image, font-face, svg |
| references), generated via the sub-resource python script in |
| ```./generic/subresource/``` (for example, loading an image: |
| ```/common/security-features/subresource/image.py?id=<UUID>```) and later verify |
| the headers used to fetch the resource. |
| |
| Since there is no way to wait for a resource referenced from CSS to be loaded, |
| all tests use ```step_timeout()``` to delay the verification step until |
| after the resource (hopefully) was loaded. |
| |
| Since there is also no way to retrieve headers (or other information) from |
| resources loaded via CSS, we store the headers with the given ```UUID``` as key |
| on the server, and retrieve them later via an XHR, for example: |
| ```/common/security-features/subresource/image.py?id=<UUID>&report-headers```. |
