First steps of &JSRef -> JSRef conversion

Replace &JSRef with JSRef in the bulk of the generated code. This will
remove a level of indirection throughout all DOM code.

This patch doesn't change methods implemented on JSRef<T> to take `self`
rather than `&self`, and it leaves a few other uses of &JSRef, but those
changes can be made incrementally.

components/script/dom/event.rs

@@ -87,7 +87,7 @@ impl Event {
                cancelable: bool) -> Temporary<Event> {
         let event = Event::new_uninitialized(global).root();
         event.deref().InitEvent(type_, can_bubble, cancelable);
-        Temporary::from_rooted(&*event)
+        Temporary::from_rooted(*event)
     }
 
     pub fn Constructor(global: &GlobalRef,