servo: Merge #14865 - Implement Subresource Integrity (from mrnayak:sri-fetch); r=jdm

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
1) Wait for response body
2) If the response does not have a termination reason and response does not match request’s integrity metadata, set response and internalResponse to a network error.

Dependency updated: html5ever-atoms from 0.1.2 to 0.1.3. This will not completely fix #14523, It will implement changes related to response validation. Request validation algorithm implementation needs CSP.

I did not update any WPT-Test. In my local system, I found some assertion issue dependent on the order of execution of test-case. It would be helpful if someone could do "try" build on these changes to get wpt results.

r? @jdm
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Source-Repo: https://github.com/servo/servo
Source-Revision: f958dafcaeed643f1232a23f5c2d4f6ba141bfea

servo/components/net_traits/request.rs

@@ -158,6 +158,7 @@ pub struct RequestInit {
     pub referrer_policy: Option<ReferrerPolicy>,
     pub pipeline_id: Option<PipelineId>,
     pub redirect_mode: RedirectMode,
+    pub integrity_metadata: String,
 }
 
 impl Default for RequestInit {
@@ -181,6 +182,7 @@ impl Default for RequestInit {
             referrer_policy: None,
             pipeline_id: None,
             redirect_mode: RedirectMode::Follow,
+            integrity_metadata: "".to_owned(),
         }
     }
 }
@@ -291,6 +293,7 @@ impl Request {
         req.referrer_policy.set(init.referrer_policy);
         req.pipeline_id.set(init.pipeline_id);
         req.redirect_mode.set(init.redirect_mode);
+        *req.integrity_metadata.borrow_mut() = init.integrity_metadata;
         req
     }