Replace all uses of the style::stylearc alias with servo_arc.

The alias is left there temporarilly and will be removed completely in a later commit where
also components/style/gecko/generated/structs_{debug|release}.rs are re-generated (they still
use the old alias).

components/script/dom/htmlobjectelement.rs

@@ -20,8 +20,8 @@ use dom::virtualmethods::VirtualMethods;
 use dom_struct::dom_struct;
 use html5ever::{LocalName, Prefix};
 use net_traits::image::base::Image;
+use servo_arc::Arc;
 use std::default::Default;
-use style::stylearc::Arc;
 
 #[dom_struct]
 pub struct HTMLObjectElement {