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"
 
 class PrefService;
 
 namespace base {
 class ListValue;
 }
 
 namespace about_flags {
 
 class FlagsStorage;
 
+// This value is reported as swtich histogram ID if switch name has unknown

[sky, 2014/08/05 16:49:14]

swtich->switch

[Alexander Alekseev, 2014/08/05 17:03:07]

Done.

+// 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 commans-line switch UMA ID, which is used in ReportCustomFlags().

[sky, 2014/08/05 16:49:14]

Returns the UMA id for the specified switch name.

[Alexander Alekseev, 2014/08/05 17:03:07]

Done.

+uint32 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.

[sky, 2014/08/05 16:49:14]

If this is only for chromeos, can we move it into the chromeos directory?

[Alexander Alekseev, 2014/08/05 17:03:07]

It was there in the first versions of this CL, but as the functionality is not
limited to ChromeOS, thestig@ advised to move it to about_flags.cc . Probably it
will be used on other OSes once.

The comment doesn't say it is limited to ChromeOS (I hope), but it just points
to the only usage for now.

There is another reason for this code to be in about_flags : because about_flags
internals depend on the ability to report a set of switches to UMA. So it
basically explains the way it is done.

+// |command_line_difference| is the result of
+// AreSwitchesIdenticalToCurrentCommandLine().
+void ReportCustomFlags(const std::string& uma_histogram_hame,
+                       const std::set<std::string>& command_line_difference);
+
+// Returns list of all command-line switches used in flags.
+std::set<std::string> GetAllSwitchesForTesting();
+
 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_