Add a metric to record http response code for download requests.

content/browser/download/download_request_core.cc

Index: content/browser/download/download_request_core.cc
diff --git a/content/browser/download/download_request_core.cc b/content/browser/download/download_request_core.cc
index 3cb2e649f34a52cace510580394c4d3cdb314b57..b30984bd52ad40c1776451ce961344c903206d33 100644
--- a/content/browser/download/download_request_core.cc
+++ b/content/browser/download/download_request_core.cc
@@ -253,6 +253,11 @@ bool DownloadRequestCore::OnResponseStarted(
                                            save_info_.get())
           : DOWNLOAD_INTERRUPT_REASON_NONE;
 
+  if (request()->response_headers()) {
+    RecordDownloadHttpResponseCode(
+        request()->response_headers()->response_code());
+  }
+
   std::unique_ptr<DownloadCreateInfo> create_info =
       CreateDownloadCreateInfo(result);
   if (result != DOWNLOAD_INTERRUPT_REASON_NONE) {