Return Fallible from get_callable_property.

components/script/dom/bindings/callback.rs

@@ -4,6 +4,7 @@
 
 //! Base classes to work with IDL callbacks.
 
+use dom::bindings::error::{Fallible, Error};
 use dom::bindings::global::global_object_for_js_object;
 use dom::bindings::js::JSRef;
 use dom::bindings::utils::Reflectable;
@@ -93,22 +94,21 @@ impl CallbackInterface {
     }
 
     /// Returns the property with the given `name`, if it is a callable object,
-    /// or `Err(())` otherwise. If it returns `Err(())`, a JSAPI exception is
-    /// pending.
+    /// or an error otherwise.
     pub fn get_callable_property(&self, cx: *mut JSContext, name: &str)
-                                 -> Result<JSVal, ()> {
+                                 -> Fallible<JSVal> {
         let mut callable = UndefinedValue();
         unsafe {
             let name = CString::new(name).unwrap();
             if JS_GetProperty(cx, self.callback(), name.as_ptr(), &mut callable) == 0 {
-                return Err(());
+                return Err(Error::JSFailed);
             }
 
             if !callable.is_object() ||
                JS_ObjectIsCallable(cx, callable.to_object()) == 0 {
                 // FIXME(#347)
                 //ThrowErrorMessage(cx, MSG_NOT_CALLABLE, description.get());
-                return Err(());
+                return Err(Error::JSFailed);
             }
         }
         Ok(callable)