Auto merge of #13058 - malisas:malisa-responseAPI, r=Manishearth,jdm

Response API

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This PR adds the [dom::Response](https://fetch.spec.whatwg.org/#response-class) implementation and addresses #11896.

The relevant passing tests` expectations have been updated.

In order to allow non-UTF-8-encoded status messages, `net_traits::response::Response`'s `raw_status` field has been changed from type [`Option<RawStatus>`](https://doc.servo.org/hyper/http/struct.RawStatus.html) to type `Option<(u16, Vec<u8>)>`. As a result, a few other files which rely on the `raw_status` field were affected and updated.

TODOs:
- The `body` and `trailer` methods. Relies on implementation of `ReadableStream` and `Promise`s.
- Similarly, replace the dummy constructor `_body: Option<USVString>` argument with `body: ResponseBodyInit`.
- Currently, whenever `r's response's header list` or `r's Headers object` are mentioned, I always modify the `headers_reflector` field (of type dom::Headers, or `r's Headers object`) and not the corresponding hyper::Headers list in the net_traits::Response field. A completely accurate interpretation of the spec might consider making both of these lists the same thing via a reference. [Discussion](https://github.com/whatwg/fetch/issues/358) was [had](https://github.com/servo/servo/pull/12884).

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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components/script/dom/bindings/trace.rs

@@ -50,6 +50,7 @@ use html5ever::tree_builder::QuirksMode;
 use hyper::header::Headers;
 use hyper::method::Method;
 use hyper::mime::Mime;
+use hyper::status::StatusCode;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
 use js::glue::{CallObjectTracer, CallUnbarrieredObjectTracer, CallValueTracer};
 use js::jsapi::{GCTraceKindToAscii, Heap, TraceKind, JSObject, JSTracer};
@@ -62,6 +63,7 @@ use net_traits::image::base::{Image, ImageMetadata};
 use net_traits::image_cache_thread::{ImageCacheChan, ImageCacheThread};
 use net_traits::request::Request;
 use net_traits::response::HttpsState;
+use net_traits::response::{Response, ResponseBody};
 use net_traits::storage_thread::StorageType;
 use net_traits::{Metadata, NetworkError, ResourceThreads};
 use offscreen_gl_context::GLLimits;
@@ -339,7 +341,10 @@ no_jsmanaged_fields!(SharedRt);
 no_jsmanaged_fields!(TouchpadPressurePhase);
 no_jsmanaged_fields!(USVString);
 no_jsmanaged_fields!(ReferrerPolicy);
+no_jsmanaged_fields!(Response);
+no_jsmanaged_fields!(ResponseBody);
 no_jsmanaged_fields!(ResourceThreads);
+no_jsmanaged_fields!(StatusCode);
 no_jsmanaged_fields!(SystemTime);
 no_jsmanaged_fields!(RelativePos);
 no_jsmanaged_fields!(OpaqueStyleAndLayoutData);