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..59b2db14d2c0a93106d53677ab8f6b40c37092ce 100644
--- a/chrome/browser/about_flags.h
+++ b/chrome/browser/about_flags.h
@@ -6,6 +6,7 @@
 #define CHROME_BROWSER_ABOUT_FLAGS_H_
 
 #include <map>
+#include <set>
 #include <string>
 
 #include "base/command_line.h"
@@ -21,6 +22,10 @@ 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,
@@ -117,9 +122,12 @@ void ConvertFlagsToSwitches(FlagsStorage* flags_storage,
 
 // 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 +168,19 @@ int GetCurrentPlatform();
 // 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.