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

chrome/browser/about_flags.h

Index: chrome/browser/about_flags.h
diff --git a/chrome/browser/about_flags.h b/chrome/browser/about_flags.h
index 55859db985106a932db1ab706f74d13f416c2512..11ccb6797e97597b612ea15af9eebff3892f0dde 100644
--- a/chrome/browser/about_flags.h
+++ b/chrome/browser/about_flags.h
@@ -6,10 +6,12 @@
 #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;
 
@@ -58,6 +60,12 @@ struct Experiment {
     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 SwitchesUmaHistogramId command_line_switch_histogram_id;
   };
 
   // The internal name of the experiment. This is never shown to the user.
@@ -85,11 +93,16 @@ struct Experiment {
   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;
@@ -109,17 +122,27 @@ struct Experiment {
 // whether it should add the sentinel switches around flags.
 enum SentinelsMode { kNoSentinels, kAddSentinels };
 
+// A simple map 'command line switch' -> 'histogram ID'.
+typedef std::map<std::string, int> SwitchesHistogramIDs;
+
 // 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 SwitchesHistogramIDs& GetSwitchesHistogramIds();
+
 // 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
@@ -160,6 +183,13 @@ int GetCurrentPlatform();
 // startup.
 void RecordUMAStatistics(FlagsStorage* flags_storage);
 
+// 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.