Rename Root<T> to DomRoot<T>

In a later PR, DomRoot<T> will become a type alias of Root<Dom<T>>,
where Root<T> will be able to handle all the things that need to be
rooted that have a stable traceable address that doesn't move for the
whole lifetime of the root. Stay tuned.

components/script/dom/promisenativehandler.rs

@@ -4,7 +4,7 @@
 
 use dom::bindings::codegen::Bindings::PromiseNativeHandlerBinding;
 use dom::bindings::reflector::{Reflector, reflect_dom_object};
-use dom::bindings::root::Root;
+use dom::bindings::root::DomRoot;
 use dom::bindings::trace::JSTraceable;
 use dom::globalscope::GlobalScope;
 use dom_struct::dom_struct;
@@ -26,7 +26,7 @@ impl PromiseNativeHandler {
     pub fn new(global: &GlobalScope,
                resolve: Option<Box<Callback>>,
                reject: Option<Box<Callback>>)
-               -> Root<PromiseNativeHandler> {
+               -> DomRoot<PromiseNativeHandler> {
         reflect_dom_object(box PromiseNativeHandler {
             reflector: Reflector::new(),
             resolve: resolve,