Auto merge of #9525 - nikkisquared:test_filtered_responses, r=asajeffrey

Test filtered responses and implement Cors Check Fetch step

I've been writing tests for creating filtered responses. So far I have three of the four types being made (namely, Basic, CORS, and Opaque), and just need to figure out how to make an OpaqueRedirect filtered response, since it's handled separately from the others. I will also add more tests to ensure the content of the filtered responses matches the limitations placed by the specification.

Along the way I implemented Cors Check, since it's required for the CORS filtered response. @jdm suggested I handle it in here, since it's such a small step, compared to other parts of Fetch.

Since all the tests currently pass, and I've spent a while adding the Cors Check and other pieces, I figured now would be a good time to start having it reviewed.

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components/net_traits/response.rs

@@ -31,7 +31,7 @@ pub enum TerminationReason {
 
 /// The response body can still be pushed to after fetch
 /// This provides a way to store unfinished response bodies
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub enum ResponseBody {
     Empty, // XXXManishearth is this necessary, or is Done(vec![]) enough?
     Receiving(Vec<u8>),
@@ -39,7 +39,7 @@ pub enum ResponseBody {
 }
 
 /// [Cache state](https://fetch.spec.whatwg.org/#concept-response-cache-state)
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub enum CacheState {
     None,
     Local,