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

chrome/browser/about_flags.h

 // 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.
 
 #ifndef CHROME_BROWSER_ABOUT_FLAGS_H_
 #define CHROME_BROWSER_ABOUT_FLAGS_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <set>
 #include <string>
 
 #include "base/command_line.h"
 #include "base/strings/string16.h"
 
 class PrefService;
 
 namespace base {
 class ListValue;
 }
 
 namespace about_flags {
 
 class FlagsStorage;
 
 // This value is reported as switch histogram ID if switch name has unknown
 // format.
-extern const uint32_t kBadSwitchFormatHistogramId;
+extern const int32_t kBadSwitchFormatHistogramId;
 
 // Enumeration of OSs.
 // This is exposed only for testing.
 enum { kOsMac = 1 << 0, kOsWin = 1 << 1, kOsLinux = 1 << 2 , kOsCrOS = 1 << 3,
        kOsAndroid = 1 << 4, kOsCrOSOwnerOnly = 1 << 5 };
 
 // Experiment is used internally by about_flags to describe an experiment (and
 // for testing).
 // This is exposed only for testing.
 struct Experiment {
@@ skipping 124 matching lines @@
 // Returns the value for the current platform. This is one of the values defined
 // by the OS enum above.
 // This is exposed only for testing.
 int GetCurrentPlatform();
 
 // Sends UMA stats about experimental flag usage. This should be called once per
 // startup.
 void RecordUMAStatistics(FlagsStorage* flags_storage);
 
 // Returns the UMA id for the specified switch name.
-uint32_t GetSwitchUMAId(const std::string& switch_name);
+int32_t GetSwitchUMAId(const std::string& switch_name);

[sky, 2014/09/02 17:13:22]

How come you aren't using  base::HistogramBase::Sample here?

[Alexander Alekseev, 2014/09/02 17:59:32]

Done.
Sorry, I missed it.

 
 // Sends stats (as UMA histogram) about command_line_difference.
 // This is used on ChromeOS to report flags that lead to browser restart.
 // |command_line_difference| is the result of
 // AreSwitchesIdenticalToCurrentCommandLine().
 void ReportCustomFlags(const std::string& uma_histogram_hame,
                        const std::set<std::string>& command_line_difference);
 
 namespace testing {
 
 // Clears internal global state, for unit tests.
 void ClearState();
 
 // Sets the list of experiments. Pass in NULL to use the default set. This does
 // NOT take ownership of the supplied Experiments.
 void SetExperiments(const Experiment* e, size_t count);
 
 // Returns the current set of experiments.
 const Experiment* GetExperiments(size_t* count);
 
 // Separator used for multi values. Multi values are represented in prefs as
 // name-of-experiment + kMultiSeparator + selected_index.
 extern const char kMultiSeparator[];
 
 }  // namespace testing
 
 }  // namespace about_flags
 
 #endif  // CHROME_BROWSER_ABOUT_FLAGS_H_