Add NetError histogram to HTTPS litepage previews

Bug: 996870
Change-Id: I26b329130c19ff8cf9811e5ac504e2c358669a83
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1766253Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689999}

chrome/browser/previews/previews_lite_page_serving_url_loader.cc

@@ -13,6 +13,7 @@
 #include "base/bind_helpers.h"
 #include "base/location.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/rand_util.h"
 #include "base/task/post_task.h"
@@ -391,6 +392,9 @@ void PreviewsLitePageServingURLLoader::OnStartLoadingResponseBody(
 
 void PreviewsLitePageServingURLLoader::OnComplete(
     const network::URLLoaderCompletionStatus& status) {
+  base::UmaHistogramSparse("Previews.ServerLitePage.ServerNetError",
+                           -status.error_code);
+
   if (forwarding_client_) {
     forwarding_client_->OnComplete(status);
     return;

tools/metrics/histograms/histograms.xml

@@ -108274,6 +108274,16 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="Previews.ServerLitePage.ServerNetError" enum="NetErrorCodes"
+    expires_after="M85">
+  <owner>robertogden@chromium.org</owner>
+  <owner>ryansturm@chromium.org</owner>
+  <summary>
+    The net error from connecting to the previews server. Recorded every time a
+    connection to the server is finished.
+  </summary>
+</histogram>
+
 <histogram name="Previews.ServerLitePage.ServerResponse"
     enum="PreviewsServerLitePageServerResponse" expires_after="2020-01-20">
   <owner>robertogden@chromium.org</owner>