auto merge of #3666 : ttaubert/servo/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.

components/script/dom/bindings/codegen/CodegenRust.py

@@ -5452,7 +5452,7 @@ class GlobalGenRoots():
                 protoDescriptor = config.getDescriptor(protoName)
                 delegate = string.Template('''impl ${selfName} for ${baseName} {
   fn ${fname}(&self) -> bool {
-    self.${parentName}.${fname}()
+    self.${parentName}().${fname}()
   }
 }
 ''').substitute({'fname': 'is_' + name.lower(),

components/script/dom/bindings/global.rs

@@ -83,7 +83,7 @@ impl<'a> GlobalRef<'a> {
     /// thread.
     pub fn script_chan<'b>(&'b self) -> &'b ScriptChan {
         match *self {
-            Window(ref window) => &window.script_chan,
+            Window(ref window) => window.script_chan(),
             Worker(ref worker) => worker.script_chan(),
         }
     }

components/script/dom/bindings/utils.rs

@@ -660,7 +660,7 @@ pub extern fn outerize_global(_cx: *mut JSContext, obj: JSHandleObject) -> *mut
                              IDLInterface::get_prototype_depth(None::<window::Window>))
             .unwrap()
             .root();
-        win.browser_context.borrow().as_ref().unwrap().window_proxy()
+        win.browser_context().as_ref().unwrap().window_proxy()
     }
 }