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/htmltabledatacellelement.rs

@@ -15,13 +15,14 @@ use servo_util::str::DOMString;
 
 #[jstraceable]
 #[must_root]
+#[privatize]
 pub struct HTMLTableDataCellElement {
-    pub htmltablecellelement: HTMLTableCellElement,
+    htmltablecellelement: HTMLTableCellElement,
 }
 
 impl HTMLTableDataCellElementDerived for EventTarget {
     fn is_htmltabledatacellelement(&self) -> bool {
-        self.type_id == NodeTargetTypeId(ElementNodeTypeId(HTMLTableDataCellElementTypeId))
+        *self.type_id() == NodeTargetTypeId(ElementNodeTypeId(HTMLTableDataCellElementTypeId))
     }
 }