Revert "Remove referer thing for now"

This reverts commit e610888.

Author: noamr

css-values-4/Overview.bs

@@ -1006,18 +1006,27 @@ URL processing model</h4>
 
 		3. Let |documentBase| be |environmentSettings|'s [=API base URL=].
 
-		4. Let |handleResourceFetchDone| be to do nothing.
+		4. Let |base| be |sheet|'s <a spec=cssom>stylesheet base URL</a>. [[CSSOM]]
 
-		5. Let |parsedUrl| be the result of the [=URL parser=] steps with |url| and |base|.
+		5. Let |referrer| be |documentBase|.
+
+		6. Let |handleResourceFetchDone| be to do nothing.
+
+		7. If |base| is null, set |base| to |documentBase|.
+
+		8. Let |parsedUrl| be the result of the [=URL parser=] steps with |url| and |base|.
 			If the algorithm returns an error, return.
 
-		6. Let |req| be a new [=/request=] whose [=request/url=] is |parsedUrl|, whose
+		9. If |corsMode| is "cors", set |referrer| to |sheet|'s
+			<a spec=cssom>location</a>. [[CSSOM]]
+
+		10. Let |req| be a new [=/request=] whose [=request/url=] is |parsedUrl|, whose
 			[=request/destination=] is |destination|, [=request/mode=] is |corsMode|,
 			[=request/origin=] is |environmentSettings|'s [=environment settings object/origin=],
 			[=request/credentials mode=] is "same-origin", [=request/use-url-credentials flag=] is
-			set, and whose [=request/referrer=] is |documentBase|.
+			set, and whose [=request/referrer=] is |referrer|.
 
-		7. [=/Fetch=] |req|, with |taskDestination| set to |global|, and |processResponseEndOfBody|
+		11. [=/Fetch=] |req|, with |taskDestination| set to |global|, and |processResponseEndOfBody|
 			set to the following steps given [=/response=] |res| and Null, failure or byte stream
 			|byteStream|:
 			1. If |sheet|'s <a spec=cssom>origin-clean flag</a> is set,