Make Response's `Clone()` method to clone headers.

This patch allows the response clone to have the same headers list as
the original's. Previously, only the cloned response's headers guard was
set to be the same as the original response's headers guard.

components/script/dom/response.rs

@@ -5,7 +5,7 @@
 use body::{BodyOperations, BodyType, consume_body, consume_body_with_promise};
 use core::cell::Cell;
 use dom::bindings::cell::DOMRefCell;
-use dom::bindings::codegen::Bindings::HeadersBinding::HeadersMethods;
+use dom::bindings::codegen::Bindings::HeadersBinding::{HeadersInit, HeadersMethods};
 use dom::bindings::codegen::Bindings::ResponseBinding;
 use dom::bindings::codegen::Bindings::ResponseBinding::{ResponseMethods, ResponseType as DOMResponseType};
 use dom::bindings::codegen::Bindings::XMLHttpRequestBinding::BodyInit;
@@ -303,6 +303,7 @@ impl ResponseMethods for Response {
         // Step 2
         let new_response = Response::new(&self.global());
         new_response.Headers().set_guard(self.Headers().get_guard());
+        try!(new_response.Headers().fill(Some(HeadersInit::Headers(self.Headers()))));
 
         // https://fetch.spec.whatwg.org/#concept-response-clone
         // Instead of storing a net_traits::Response internally, we

tests/wpt/metadata/fetch/api/response/response-clone.html.ini

@@ -1,8 +1,5 @@
 [response-clone.html]
   type: testharness
-  [Check Response's clone has the expected attribute values]
-    expected: FAIL
-
   [Check orginal response's body after cloning]
     expected: FAIL