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

content/browser/download/download_stats.cc

Index: content/browser/download/download_stats.cc
diff --git a/content/browser/download/download_stats.cc b/content/browser/download/download_stats.cc
index d859b2804acc79a223d6036a18adc9997698cd32..80be40f4e3e4849ac5ddbd5696f55f516f334690 100644
--- a/content/browser/download/download_stats.cc
+++ b/content/browser/download/download_stats.cc
@@ -12,6 +12,7 @@
 #include "content/browser/download/download_resource_handler.h"
 #include "content/public/browser/download_interrupt_reasons.h"
 #include "net/http/http_content_disposition.h"
+#include "net/http/http_util.h"
 
 namespace content {
 
@@ -932,4 +933,11 @@ void RecordDownloadSourcePageTransitionType(
       ui::PAGE_TRANSITION_LAST_CORE + 1);
 }
 
+void RecordDownloadHttpResponseCode(int response_code) {
+  UMA_HISTOGRAM_CUSTOM_ENUMERATION(
+      "Download.HttpResponseCode",
+      net::HttpUtil::MapStatusCodeForHistogram(response_code),
+      net::HttpUtil::GetStatusCodesForHistogram());
+}
+
 }  // namespace content