Fix up certificate error reporting histograms

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"
@@ skipping 87 matching lines @@
   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.
+// fail to send.
 void RecordUMAOnFailure(const GURL& report_uri, int net_error) {
-  UMA_HISTOGRAM_SPARSE_SLOWLY("SSL.ExpectCTReportFailure", net_error);
+  UMA_HISTOGRAM_SPARSE_SLOWLY("SSL.ExpectCTReportFailure", -net_error);

[felt, 2016/07/01 22:05:58]

Will this change the histogram? Do you need to define a new histogram to avoid
messed up results in the transition?

[estark, 2016/07/01 22:08:53]

It will change it, but I think it's okay. I'm pretty sure I'm the only one
looking at these, and it just means that for a while we'll have to add two
numbers together (the negative version and the positive version) to get the full
count for a given error code. Maybe I should add a note to the histograms.xml
description?

[felt, 2016/07/01 22:13:48]

If you're the only one looking at it, probably fine, but please do add a note.

 }
 
 }  // namespace
 
 ChromeExpectCTReporter::ChromeExpectCTReporter(
     net::URLRequestContext* request_context)
     : report_sender_(
           new net::ReportSender(request_context,
                                 net::ReportSender::DO_NOT_SEND_COOKIES,
                                 base::Bind(RecordUMAOnFailure))) {}
@@ skipping 49 matching lines @@
   std::string serialized_report;
   if (!base::JSONWriter::Write(report, &serialized_report)) {
     LOG(ERROR) << "Failed to serialize Expect CT report";
     return;
   }
 
   UMA_HISTOGRAM_BOOLEAN("SSL.ExpectCTReportSendingAttempt", true);
 
   report_sender_->Send(report_uri, serialized_report);
 }