[NTP Snippets] Add metric for fetch error cases

components/ntp_snippets/ntp_snippets_fetcher.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/ntp_snippets/ntp_snippets_fetcher.h"
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
+#include "base/metrics/sparse_histogram.h"
 #include "base/path_service.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/task_runner_util.h"
 #include "google_apis/google_api_keys.h"
 #include "net/base/load_flags.h"
 #include "net/http/http_request_headers.h"
 #include "net/http/http_response_headers.h"
 #include "net/http/http_status_code.h"
@@ skipping 94 matching lines @@
   url_fetcher_->Start();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // URLFetcherDelegate overrides
 void NTPSnippetsFetcher::OnURLFetchComplete(const URLFetcher* source) {
   DCHECK_EQ(url_fetcher_.get(), source);
 
   std::string message;
   const URLRequestStatus& status = source->GetStatus();
+
+  UMA_HISTOGRAM_SPARSE_SLOWLY(
+      "NewTabPage.Snippets.FetchHttpResponseOrErrorCode",
+      status.is_success() ? source->GetResponseCode() : status.error());
+
   if (!status.is_success()) {
     message = base::StringPrintf(kStatusMessageURLRequestErrorFormat,
                                  status.error());
   } else if (source->GetResponseCode() != net::HTTP_OK) {
     message = base::StringPrintf(kStatusMessageHTTPErrorFormat,
                                  source->GetResponseCode());
   }
 
   std::string response;
   if (!message.empty()) {
     DLOG(WARNING) << message << " while trying to download "
                   << source->GetURL().spec();
 
   } else {
     bool stores_result_to_string = source->GetResponseAsString(&response);
     DCHECK(stores_result_to_string);
   }
 
   callback_list_.Notify(response, message);
 }
 
 }  // namespace ntp_snippets