Collect UMA statistics on which chrome://flags lead to chrome restart on ChromeOS.

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;
+
 // 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 {
   enum Type {
@@ skipping 76 matching lines @@
 enum SentinelsMode { kNoSentinels, kAddSentinels };
 
 // Reads the Labs |prefs| (called "Labs" for historical reasons) and adds the
 // commandline flags belonging to the active experiments to |command_line|.
 void ConvertFlagsToSwitches(FlagsStorage* flags_storage,
                             base::CommandLine* command_line,
                             SentinelsMode sentinels);
 
 // Compares a set of switches of the two provided command line objects and
 // returns true if they are the same and false otherwise.
+// If |out_difference| is not NULL, it's filled with set_symmetric_difference
+// between sets.
 bool AreSwitchesIdenticalToCurrentCommandLine(
     const base::CommandLine& new_cmdline,
-    const base::CommandLine& active_cmdline);
+    const base::CommandLine& active_cmdline,
+    std::set<CommandLine::StringType>* out_difference);
 
 // Differentiate between generic flags available on a per session base and flags
 // that influence the whole machine and can be said by the admin only. This flag
 // is relevant for ChromeOS for now only and dictates whether entries marked
 // with the |kOsCrOSOwnerOnly| label should be enabled in the UI or not.
 enum FlagAccess { kGeneralAccessFlagsOnly, kOwnerAccessToFlags };
 
 // Get the list of experiments. Experiments that are available on the current
 // platform are appended to |supported_experiments|; all other experiments are
 // appended to |unsupported_experiments|.
@@ skipping 20 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);
+
+// 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_