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

chrome/browser/chromeos/login/login_utils.cc

Index: chrome/browser/chromeos/login/login_utils.cc
diff --git a/chrome/browser/chromeos/login/login_utils.cc b/chrome/browser/chromeos/login/login_utils.cc
index fafe4398fe5abc26626f9aadd4c18c42f612460f..e13a94d8a45c3909d77180b514dc854ffc16eb59 100644
--- a/chrome/browser/chromeos/login/login_utils.cc
+++ b/chrome/browser/chromeos/login/login_utils.cc
@@ -40,6 +40,7 @@
 #include "chrome/browser/chromeos/login/demo_mode/demo_app_launcher.h"
 #include "chrome/browser/chromeos/login/lock/screen_locker.h"
 #include "chrome/browser/chromeos/login/profile_auth_data.h"
+#include "chrome/browser/chromeos/login/report_restarting_flags.h"
 #include "chrome/browser/chromeos/login/saml/saml_offline_signin_limiter.h"
 #include "chrome/browser/chromeos/login/saml/saml_offline_signin_limiter_factory.h"
 #include "chrome/browser/chromeos/login/session/session_manager.h"
@@ -85,7 +86,6 @@
 #include "url/gurl.h"
 
 using content::BrowserThread;
-
 namespace chromeos {
 
 struct DoBrowserLaunchOnLocaleLoadedData;
@@ -216,16 +216,29 @@ void LoginUtilsImpl::DoBrowserLaunchOnLocaleLoadedImpl(
   about_flags::PrefServiceFlagsStorage flags_storage_(profile->GetPrefs());
   about_flags::ConvertFlagsToSwitches(&flags_storage_, &user_flags,
                                       about_flags::kAddSentinels);
+
+  // about_flags::AreSwitchesIdenticalToCurrentCommandLine() requires
+  // output argument to be std::set<CommandLine::StringType>* .
+  // To report the difference, we need std::set<std::string> .
+  // So here we are silently using the fact, that CommandLine::StringType
+  // is std::string on ChromeOS. Otherwise we would have to decode strings here.
+  std::set<std::string> command_line_difference;
+
   // Only restart if needed and if not going into managed mode.
   // Don't restart browser if it is not first profile in session.
   if (UserManager::Get()->GetLoggedInUsers().size() == 1 &&
       !UserManager::Get()->IsLoggedInAsLocallyManagedUser() &&
       !about_flags::AreSwitchesIdenticalToCurrentCommandLine(
-          user_flags, *CommandLine::ForCurrentProcess())) {
+          user_flags,
+          *CommandLine::ForCurrentProcess(),
+          &command_line_difference)) {
     CommandLine::StringVector flags;
     // argv[0] is the program name |CommandLine::NO_PROGRAM|.
     flags.assign(user_flags.argv().begin() + 1, user_flags.argv().end());
     VLOG(1) << "Restarting to apply per-session flags...";
+
+    ReportRestartingFlags(command_line_difference);
+
     DBusThreadManager::Get()->GetSessionManagerClient()->SetFlagsForUser(
         UserManager::Get()->GetActiveUser()->email(), flags);
     AttemptRestart(profile);