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..98803ff2d8b2e02585f1d4ca692ae22df90a5637 100644
--- a/chrome/browser/chromeos/login/login_utils.cc
+++ b/chrome/browser/chromeos/login/login_utils.cc
@@ -19,6 +19,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
 #include "base/memory/weak_ptr.h"
+#include "base/metrics/sparse_histogram.h"
 #include "base/prefs/pref_member.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/string_util.h"
@@ -85,11 +86,50 @@
 #include "url/gurl.h"
 
 using content::BrowserThread;
-
 namespace chromeos {
 
 struct DoBrowserLaunchOnLocaleLoadedData;
 
+namespace {
+
+void ReportCustomFlags(const std::set<std::string>& command_line_difference) {
+  const about_flags::SwitchesHistogramIDs& switch_histogram_id_map =
+      about_flags::GetSwitchesHistogramIds();
+  for (std::set<std::string>::const_iterator it =
+           command_line_difference.begin();
+       it != command_line_difference.end();
+       ++it) {
+    int uma_id = about_flags::UMA_HISTOGRAM_ID_UNKNOWN_FLAG;
+    if (it->size() > 2) {
+      // skip '--' before switch name
+      std::string switch_name(it->substr(2));
+
+      // kill value, if any
+      const size_t value_pos = switch_name.find('=');
+      if (value_pos != std::string::npos)
+        switch_name.resize(value_pos);
+
+      const about_flags::SwitchesHistogramIDs::const_iterator pos =
+          switch_histogram_id_map.find(switch_name);
+      if (pos != switch_histogram_id_map.end()) {
+        uma_id = pos->second;
+      } else {
+        uma_id = about_flags::UMA_HISTOGRAM_ID_UNKNOWN_FLAG;
+        LOG(ERROR) << "ReportCustomFlags(): flag '" << *it << "' ('"
+                   << switch_name << "') is unknown.";
+      }
+    } else {
+      uma_id = about_flags::UMA_HISTOGRAM_ID_BAD_FLAG_FORMAT;
+      LOG(ERROR) << "ReportCustomFlags(): flag '" << *it
+                 << "' has incorrect format.";
+    }
+    VLOG(1) << "ReportCustomFlags(): '" << *it << "', uma_id=" << uma_id;
+    UMA_HISTOGRAM_SPARSE_SLOWLY("Login.CustomFlags", uma_id);

[Alexei Svitkine (slow), 2014/07/02 17:45:40]

Wouldn't this histogram be useful on other platforms too, not just CrOS?

Could it be put in some common startup code?

[Alexander Alekseev, 2014/07/02 17:55:03]

thestig@: Do you think it is reasonable to create new file:

chrome/browser/about_flags_report_custom_flags.cc ?

[Lei Zhang, 2014/07/02 19:01:04]

Would about_flags_report_custom_flags.cc just have ReportCustomFlags() in it?
How about just adding it to about_flags.cc?

+  }
+}
+
+}  // namespace
+
 class LoginUtilsImpl
     : public LoginUtils,
       public base::SupportsWeakPtr<LoginUtilsImpl>,
@@ -216,16 +256,24 @@ void LoginUtilsImpl::DoBrowserLaunchOnLocaleLoadedImpl(
   about_flags::PrefServiceFlagsStorage flags_storage_(profile->GetPrefs());
   about_flags::ConvertFlagsToSwitches(&flags_storage_, &user_flags,
                                       about_flags::kAddSentinels);
+
+  std::set<CommandLine::StringType> 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...";
+
+    ReportCustomFlags(command_line_difference);
+
     DBusThreadManager::Get()->GetSessionManagerClient()->SetFlagsForUser(
         UserManager::Get()->GetActiveUser()->email(), flags);
     AttemptRestart(profile);