DNR: Improve documentation for "domains" and "excludedDomains".

Make it explicit that these fields match the request initiator.

BUG=1120739

Change-Id: I380def94e0a92a8aa6a523896f146d3b27579b84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2388775
Auto-Submit: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Kelvin Jiang <kelvinjiang@chromium.org>
Commit-Queue: Kelvin Jiang <kelvinjiang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804035}

extensions/common/api/declarative_net_request.idl

@@ -199,18 +199,30 @@ namespace declarativeNetRequest {
     // <code>domains</code>. If the list is omitted, the rule is applied to
     // requests from all domains. An empty list is not allowed.
     //
-    // Note: sub-domains like "a.example.com" are also allowed.
-    // The entries must consist of only ascii characters. Use punycode encoding
-    // for internationalized domains.
+    // Notes:
+    // <ul>
+    //  <li>Sub-domains like "a.example.com" are also allowed.</li>
+    //  <li>The entries must consist of only ascii characters.</li>
+    //  <li>Use punycode encoding for internationalized domains.</li>
+    //  <li>
+    //    This matches against the request initiator and not the request url.
+    //  </li>
+    // </ul>
     DOMString[]? domains;
 
     // The rule will not match network requests originating from the list of
-    // <code> excludedDomains</code>. If the list is empty or omitted, no domains
-    // are excluded. This takes precedence over <code> domains</code>.
+    // <code>excludedDomains</code>. If the list is empty or omitted, no
+    // domains are excluded. This takes precedence over <code>domains</code>.
     //
-    // Note: sub-domains like "a.example.com" are also allowed.
-    // The entries must consist of only ascii characters. Use punycode encoding
-    // for internationalized domains.
+    // Notes:
+    // <ul>
+    //  <li>Sub-domains like "a.example.com" are also allowed.</li>
+    //  <li>The entries must consist of only ascii characters.</li>
+    //  <li>Use punycode encoding for internationalized domains.</li>
+    //  <li>
+    //    This matches against the request initiator and not the request url.
+    //  </li>
+    // </ul>
     DOMString[]? excludedDomains;
 
     // List of resource types which the rule can match. An empty list is not