about_flags::ReportCustomFlags() should use signed 32-bit IDs.

chrome/browser/about_flags.cc

 // Copyright (c) 2012 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/about_flags.h"
 
 #include <iterator>
 #include <map>
 #include <set>
 #include <utility>
@@ skipping 2221 matching lines @@
     content::RecordComputedAction(action);
   }
   // Since flag metrics are recorded every startup, add a tick so that the
   // stats can be made meaningful.
   if (flags.size())
     content::RecordAction(UserMetricsAction("AboutFlags_StartupTick"));
   content::RecordAction(UserMetricsAction("StartupTick"));
 }
 
 uint32_t GetSwitchUMAId(const std::string& switch_name) {
-  return static_cast<uint32_t>(metrics::HashMetricName(switch_name));
+  // Need to strip sign bit.

[sky, 2014/08/27 20:24:53]

You need a better comment. Document 'why' we need to strip the sign bit, not
what the code is doing.

[Alexander Alekseev, 2014/08/28 02:48:55]

Done.

+  return static_cast<uint32_t>(metrics::HashMetricName(switch_name)) &

[Ilya Sherman, 2014/08/27 22:05:20]

Why not just static_cast to <int32_t>?  That has the added benefit that you'd
maintain consistency with the data that's currently being uploaded.

[Alexander Alekseev, 2014/08/28 02:48:55]

static_cast<int32_t>((uint64_t)(-1LL)) == -1

So I changed the return type, but AND is still needed here.

[Ilya Sherman, 2014/08/28 03:49:57]

I don't understand the problem.  What's wrong with reporting -1?

[Alexander Alekseev, 2014/08/28 14:40:52]

Except that it is unnatural, nothing wrong. Done.

PS: BTW, pretty-print.py formats comments inside enum with negative values
incorrectly. So this histograms.xml is uploaded with bypass-hooks option.

+         std::numeric_limits<int32_t>::max();
 }
 
 void ReportCustomFlags(const std::string& uma_histogram_hame,
                        const std::set<std::string>& command_line_difference) {
   for (std::set<std::string>::const_iterator it =
            command_line_difference.begin();
        it != command_line_difference.end();
        ++it) {
     int uma_id = about_flags::kBadSwitchFormatHistogramId;
     if (StartsWithASCII(*it, "--", true /* case_sensitive */)) {
@@ skipping 211 matching lines @@
 }
 
 const Experiment* GetExperiments(size_t* count) {
   *count = num_experiments;
   return experiments;
 }
 
 }  // namespace testing
 
 }  // namespace about_flags