servo: Merge #3666 - Privatize DOM (fixes #3644) (from ttaubert:issue/3644-privatize-dom); r=Manishearth

This PR removes public fields from all (hope I didn't miss any) DOM structs. Should |Page| be privatized as well? This PR additionally introduces a #[privatize] lint to ensure nobody accidentally re-introduces a public field.

All changesets compile separately if applied in the same order. Hope that helps reviewing but I can of course squash them before merging.

Source-Repo: https://github.com/servo/servo
Source-Revision: f350879574194bb612eac88e21d0920e9827afa7

servo/components/script/dom/documentfragment.rs

@@ -20,13 +20,14 @@ use servo_util::str::DOMString;
 
 #[jstraceable]
 #[must_root]
+#[privatize]
 pub struct DocumentFragment {
-    pub node: Node,
+    node: Node,
 }
 
 impl DocumentFragmentDerived for EventTarget {
     fn is_documentfragment(&self) -> bool {
-        self.type_id == NodeTargetTypeId(DocumentFragmentNodeTypeId)
+        *self.type_id() == NodeTargetTypeId(DocumentFragmentNodeTypeId)
     }
 }