This commit allows headers with "content-type" name to be classified as valid header name, depending on its value according to [the Fetch spec](https://fetch.spec.whatwg.org/#cors-safelisted-request-header). As a result of this change, more request web platform tests pass, whose expected test results are updated with this commit.
This commit modifies the headers API script to correctly validate value. As a result of this change, more wpt tests pass. The commit also changes the expected test results.
This commit adds new files related to implementing the [Request
API](https://fetch.spec.whatwg.org/#request-class). This commit also
changes the expected web platform tests results. It also modifies the
following files:
components/net_traits/request.rs
HeapSizeOf is implemented in net_traits/request so that dom::request can
be used as a wrapper around net_traits::request::Request.
components/script/dom/headers.rs
Several methods are added to Headers so that request can access and
modify some of the headers fields.
- Reworked the append method to support the inner `hyper::header::Headers`'s HashMap `insert` method, which overwrites entries instead of appending.
- Filled out constructor as well as delete, get, has, and set methods.
- Updated relevant test expectations
