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 <map>
+#include <set>
 #include <string>
 
 #include "base/command_line.h"
 #include "base/strings/string16.h"
+#include "chrome/browser/about_flags_switches_histogram_ids.h"
 
 class PrefService;
 
 namespace base {
 class ListValue;
 }
 
 namespace about_flags {
 
 class FlagsStorage;
@@ skipping 28 matching lines @@
   // Used for MULTI_VALUE types to describe one of the possible values the user
   // can select.
   struct Choice {
     // ID of the message containing the choice name.
     int description_id;
 
     // Command line switch and value to enabled for this choice.
     const char* command_line_switch;
     // Simple switches that have no value should use "" for command_line_value.
     const char* command_line_value;
+
+    // ID of command_line_switch in UMA histograms.
+    // On ChromeOS experiments lead to chrome process restart when user logs in.
+    // IDs of switches that lead to restart are reported.
+    // Must be zero for entries without command_line_switches.
+    const int command_line_switch_histogram_id;
   };
 
   // The internal name of the experiment. This is never shown to the user.
   // It _is_ however stored in the prefs file, so you shouldn't change the
   // name of existing flags.
   const char* internal_name;
 
   // String id of the message containing the experiment's name.
   int visible_name_id;
 
   // String id of the message containing the experiment's description.
   int visible_description_id;
 
   // The platforms the experiment is available on
   // Needs to be more than a compile-time #ifdef because of profile sync.
   unsigned supported_platforms;  // bitmask
 
   // Type of experiment.
   Type type;
 
   // The commandline switch and value that are added when this flag is active.
   // This is different from |internal_name| so that the commandline flag can be
   // renamed without breaking the prefs file.
   // This is used if type is SINGLE_VALUE or ENABLE_DISABLE_VALUE.
   const char* command_line_switch;
   // Simple switches that have no value should use "" for command_line_value.
   const char* command_line_value;
+  // ID of command_line_switch in UMA histograms.
+  // (See Choice::command_line_switch_histogram_id.)
+  // Must be zero for entries without command_line_switches.
+  const int command_line_switch_histogram_id;
 
   // For ENABLE_DISABLE_VALUE, the command line switch and value to explictly
   // disable the feature.
   const char* disable_command_line_switch;
   const char* disable_command_line_value;
+  const int disable_command_line_switch_histogram_id;
 
   // This is used if type is MULTI_VALUE.
   const Choice* choices;
 
   // Number of |choices|.
   // This is used if type is MULTI_VALUE.
   int num_choices;
 
   // Returns the name used in prefs for the choice at the specified |index|.
   std::string NameForChoice(int index) const;
 
   // Returns the human readable description for the choice at |index|.
   base::string16 DescriptionForChoice(int index) const;
 };
 
 // A flag controlling the behavior of the |ConvertFlagsToSwitches| function -
 // whether it should add the sentinel switches around flags.
 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);
 
+// Returns a map <command_line_switch, switch_histogram_id>.
+// Map is created if it doesn't exist.
+const std::map<std::string, int>& GetSwitchesHistogramIds();

[Lei Zhang, 2014/06/27 19:46:44]

Having "typedef std::map<std::string, int> SwitchesHistogramMap" makes the code
slightly more readable and saves a few letters.

[Alexander Alekseev, 2014/06/30 15:06:01]

Done.

+
 // 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 41 matching lines @@
 
 // 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_