DNR: Add some documentation for allowAllRequests rules.

More documentation/examples will follow once the documentation for generic
priority lands.

BUG=1038831

Change-Id: I88cf351a6c327c6dbcf8554cf71a17ee82b06933
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2001755
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734329}

chrome/common/extensions/docs/templates/intros/declarativeNetRequest.html

@@ -337,6 +337,7 @@ are true:
 </pre>
 
 <ul>
+  <!--TODO(crbug.com/1038831): Add examples for allowAllRequests rules. -->
   <li>
     Consider a navigation to <code>"http://google.com"</code>. Rules with id (1)
     and (3) match. The request will be blocked because blocking rules have

extensions/common/api/declarative_net_request.idl

@@ -54,9 +54,8 @@ namespace declarativeNetRequest {
     upgradeScheme,
     // Remove request/response headers from the network request.
     removeHeaders,
-    // TODO(crbug.com/1038831): Add documentation once the implementation is
-    // complete.
-    [nodoc]
+    // Allow all requests within a frame hierarchy, including the frame request
+    // itself.
     allowAllRequests
   };
 
@@ -182,6 +181,10 @@ namespace declarativeNetRequest {
 
     // List of resource types which the rule can match. An empty list is not
     // allowed.
+    //
+    // Note: this must be specified for <code>allowAllRequests</code> rules and
+    // may only include the <code>sub_frame</code> and <code>main_frame</code>
+    // resource types.
     ResourceType[]? resourceTypes;
 
     // List of resource types which the rule won't match. Only one of