Implement Subresource Integrity

Implemented response validation part of
https://w3c.github.io/webappsec-subresource-integrity/.
Implemented step eighteen of the main fetch. If a request has integrity
metadata, then following steps are performed
*Wait for response body
*If the response does not have a termination reason and response does not
match request’s integrity metadata, set response to a
network error.# Please enter the commit message for your changes. Lines starting

tests/unit/net/lib.rs

@@ -33,6 +33,7 @@ extern crate url;
 #[cfg(test)] mod hsts;
 #[cfg(test)] mod http_loader;
 #[cfg(test)] mod filemanager_thread;
+#[cfg(test)] mod subresource_integrity;
 
 use devtools_traits::DevtoolsControlMsg;
 use hyper::server::{Handler, Listening, Server};