Collect the end-state of keepalive requests, with redirect count

Proposal: https://docs.google.com/document/d/1XYsa2W1zjWIvrpuAq7IA1wEGZIvbJLoiPF6rMob01Tg/edit

Bug: 1147816
Change-Id: I0c030b7ba142ceb72a4cc8a2425bad2118689f9a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532016
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Auto-Submit: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Dominic Battré <battre@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827776}

extensions/browser/api/web_request/web_request_proxying_url_loader_factory.cc

@@ -156,6 +156,7 @@ WebRequestProxyingURLLoaderFactory::InProgressRequest::~InProgressRequest() {
       ukm::builders::Extensions_WebRequest_KeepaliveRequestFinished(
           ukm_source_id_)
           .SetState(state_)
+          .SetNumRedirects(num_redirects_)
           .Record(ukm::UkmRecorder::Get());
     }
   }
@@ -306,6 +307,7 @@ void WebRequestProxyingURLLoaderFactory::InProgressRequest::FollowRedirect(
     }
   }
 
+  ++num_redirects_;
   RestartInternal();
 }
 

extensions/browser/api/web_request/web_request_proxying_url_loader_factory.h

@@ -197,6 +197,8 @@ class WebRequestProxyingURLLoaderFactory
     // lifetime.
     base::Optional<net::AuthCredentials> auth_credentials_;
 
+    int num_redirects_ = 0;
+
     const bool for_cors_preflight_ = false;
 
     // If |has_any_extra_headers_listeners_| is set to true, the request will be

tools/metrics/ukm/ukm.xml

@@ -4297,6 +4297,19 @@ be describing additional metrics about the same event.
     Whether and how keepalive requests are blocked. Recorded when a keepalive
     request finishes.
   </summary>
+  <metric name="NumRedirects">
+    <summary>
+      The number of redirects the request experienced. This is up to 21, as
+      specified at https://fetch.spec.whatwg.org/#http-redirect-fetch .
+    </summary>
+    <aggregation>
+      <history>
+        <statistics>
+          <enumeration/>
+        </statistics>
+      </history>
+    </aggregation>
+  </metric>
   <metric name="State" enum="ExtensionInProgressRequestState">
     <summary>
       The final state of the request.