Comment 7 for bug 973646

All g_assert here should be g_return_if_fail. It's better to have warnings than crash the browser if something's wrong.

The updated check on the data source looks good.

The refactoring of the function would be nice to keep separate if that's fine with you. Otherwise it's harder to see the key changes in the history later. The WEBKIT_POLICY_ERROR_FRAME_LOAD_INTERRUPTED_BY_POLICY_CHANGE should also be separate for the same reason, it's a small detail that would disappear in the whole.