The Gtk DRT needs resourced load callbacks to pass some tests. For example the tests: * http/tests/loading/resource-methods.html * http/tests/misc/favicons-loads-with-images-disabled.html ... require these callbacks to match the expected result. There are probably more tests that require it. The callbacks may also be helpful for embedders to know if certain esources were loaded, etc...
One more test: http/tests/cache/subresource-failover-to-network.html
These tests are not skipped any longer.