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

Response API

<!-- Please describe your changes on the following line: -->
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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1 files changed, 11 insertions, 5 deletions

diff --git a/components/script/dom/headers.rs b/components/script/dom/headers.rs
index 7b45956c039..abfa959c8e6 100644
--- a/components/script/dom/headers.rs
+++ b/components/script/dom/headers.rs
@@ -209,7 +209,13 @@ impl Headers {
         headers_for_request
     }
 
-     pub fn set_guard(&self, new_guard: Guard) {
+    pub fn for_response(global: GlobalRef) -> Root<Headers> {
+        let headers_for_response = Headers::new(global);
+        headers_for_response.guard.set(Guard::Response);
+        headers_for_response
+    }
+
+    pub fn set_guard(&self, new_guard: Guard) {
         self.guard.set(new_guard)
     }
 
@@ -346,7 +352,7 @@ pub fn is_forbidden_header_name(name: &str) -> bool {
 // [3] https://tools.ietf.org/html/rfc7230#section-3.2.6
 // [4] https://www.rfc-editor.org/errata_search.php?rfc=7230
 fn validate_name_and_value(name: ByteString, value: ByteString)
-                           -> Result<(String, Vec<u8>), Error> {
+                           -> Fallible<(String, Vec<u8>)> {
     let valid_name = try!(validate_name(name));
     if !is_field_content(&value) {
         return Err(Error::Type("Value is not valid".to_string()));
@@ -354,7 +360,7 @@ fn validate_name_and_value(name: ByteString, value: ByteString)
     Ok((valid_name, value.into()))
 }
 
-fn validate_name(name: ByteString) -> Result<String, Error> {
+fn validate_name(name: ByteString) -> Fallible<String> {
     if !is_field_name(&name) {
         return Err(Error::Type("Name is not valid".to_string()));
     }
@@ -444,7 +450,7 @@ fn is_field_vchar(x: u8) -> bool {
 }
 
 // https://tools.ietf.org/html/rfc5234#appendix-B.1
-fn is_vchar(x: u8) -> bool {
+pub fn is_vchar(x: u8) -> bool {
     match x {
         0x21...0x7E => true,
         _ => false,
@@ -452,7 +458,7 @@ fn is_vchar(x: u8) -> bool {
 }
 
 // http://tools.ietf.org/html/rfc7230#section-3.2.6
-fn is_obs_text(x: u8) -> bool {
+pub fn is_obs_text(x: u8) -> bool {
     match x {
         0x80...0xFF => true,
         _ => false,