Add UMA metric for Expect CT failure

chrome/browser/ssl/chrome_expect_ct_reporter.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 "chrome/browser/ssl/chrome_expect_ct_reporter.h"
 
 #include <string>
 
 #include "base/base64.h"
 #include "base/command_line.h"
 #include "base/feature_list.h"
 #include "base/json/json_writer.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/metrics/sparse_histogram.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "base/values.h"
 #include "chrome/common/chrome_features.h"
 #include "net/url_request/certificate_report_sender.h"
 
 namespace {
 
 std::string TimeToISO8601(const base::Time& t) {
   base::Time::Exploded exploded;
@@ skipping 71 matching lines @@
   base::Base64Encode(sct_and_status.sct->extensions, &extensions);
   sct->SetString("extensions", extensions);
   std::string signature;
   base::Base64Encode(sct_and_status.sct->signature.signature_data, &signature);
   sct->SetString("signature", signature);
 
   list_item->Set("sct", std::move(sct));
   list->Append(std::move(list_item));
 }
 
+// Records an UMA histogram of the net errors when Expect CT reports
+// fails to send.
+void RecordUMAOnFailure(const GURL& report_uri, int net_error) {
+  UMA_HISTOGRAM_SPARSE_SLOWLY("SSL.ExpectCTReportFailure", net_error);
+}
+
 }  // namespace
 
 ChromeExpectCTReporter::ChromeExpectCTReporter(
     net::URLRequestContext* request_context)
     : report_sender_(new net::CertificateReportSender(
           request_context,
-          net::CertificateReportSender::DO_NOT_SEND_COOKIES)) {}
+          net::CertificateReportSender::DO_NOT_SEND_COOKIES,
+          base::Bind(RecordUMAOnFailure))) {}
 
 ChromeExpectCTReporter::~ChromeExpectCTReporter() {}
 
 void ChromeExpectCTReporter::OnExpectCTFailed(
     const net::HostPortPair& host_port_pair,
     const GURL& report_uri,
     const net::SSLInfo& ssl_info) {
   if (report_uri.is_empty())
     return;
 
@@ skipping 37 matching lines @@
   report.Set("valid-scts", std::move(valid_scts));
 
   std::string serialized_report;
   if (!base::JSONWriter::Write(report, &serialized_report)) {
     LOG(ERROR) << "Failed to serialize Expect CT report";
     return;
   }
 
   report_sender_->Send(report_uri, serialized_report);
 }