Migrate startup URLs pref.

chrome/browser/prefs/session_startup_pref.cc

Index: chrome/browser/prefs/session_startup_pref.cc
diff --git a/chrome/browser/prefs/session_startup_pref.cc b/chrome/browser/prefs/session_startup_pref.cc
index 478790a157d1c44ab61dc8fc84c2fae754dba090..d40fa2489b82a477e6dbc5c81b1457d9282cfb01 100644
--- a/chrome/browser/prefs/session_startup_pref.cc
+++ b/chrome/browser/prefs/session_startup_pref.cc
@@ -6,7 +6,9 @@
 
 #include <string>
 
+#include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
+#include "base/time/time.h"
 #include "base/values.h"
 #include "base/version.h"
 #include "chrome/browser/prefs/scoped_user_pref_update.h"
@@ -21,6 +23,13 @@
 
 namespace {
 
+enum StartupURLsMigrationMetrics {
+  STARTUP_URLS_MIGRATION_METRICS_STARTED,
+  STARTUP_URLS_MIGRATION_METRICS_DELETED,
+  STARTUP_URLS_MIGRATION_METRICS_RESET,
+  STARTUP_URLS_MIGRATION_METRICS_MAX,
+};
+
 // Converts a SessionStartupPref::Type to an integer written to prefs.
 int TypeToPrefValue(SessionStartupPref::Type type) {
   switch (type) {
@@ -62,10 +71,16 @@ void SessionStartupPref::RegisterProfilePrefs(
       user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
   registry->RegisterListPref(prefs::kURLsToRestoreOnStartup,
                              user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
+  registry->RegisterListPref(prefs::kURLsToRestoreOnStartupOld,
+                             user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
   registry->RegisterBooleanPref(
       prefs::kRestoreOnStartupMigrated,
       false,
       user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
+  registry->RegisterDoublePref(
+      prefs::kRestoreStartupURLsMigrated,
+      false,
+      user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
 }
 
 // static
@@ -136,8 +151,51 @@ SessionStartupPref SessionStartupPref::GetStartupPref(PrefService* prefs) {
 void SessionStartupPref::MigrateIfNecessary(PrefService* prefs) {
   DCHECK(prefs);
 
+  // Check if we need to migrate the old version of the startup URLs preference
+  // to the new name, and also send metrics about the migration.
+  const base::ListValue* old_startup_urls =
+      prefs->GetList(prefs::kURLsToRestoreOnStartupOld);
+  if (!prefs->GetUserPrefValue(prefs::kRestoreStartupURLsMigrated)) {
+    // Seems like we never migrated, do it if necessary.
+    if (!prefs->GetUserPrefValue(prefs::kURLsToRestoreOnStartup)) {
+      if (old_startup_urls && old_startup_urls->GetSize() > 0) {
+        prefs->Set(prefs::kURLsToRestoreOnStartup, *old_startup_urls);
+        prefs->Set(prefs::kURLsToRestoreOnStartupOld, base::ListValue());
+      }
+      UMA_HISTOGRAM_ENUMERATION(
+          "Settings.StartupURLsMigration",
+          STARTUP_URLS_MIGRATION_METRICS_STARTED,
+          STARTUP_URLS_MIGRATION_METRICS_MAX);
+    } else {
+      // We migrated but the migration data got deleted somehow.
+      UMA_HISTOGRAM_ENUMERATION(
+          "Settings.StartupURLsMigration",
+          STARTUP_URLS_MIGRATION_METRICS_DELETED,
+          STARTUP_URLS_MIGRATION_METRICS_MAX);
+    }
+    prefs->SetDouble(prefs::kRestoreStartupURLsMigrated,
+                     base::Time::Now().ToDoubleT());
+  } else if (old_startup_urls && old_startup_urls->GetSize() > 0) {
+    // Migration needs to be reset.
+    prefs->Set(prefs::kURLsToRestoreOnStartupOld, base::ListValue());
+    base::Time last_migration_time = base::Time::FromDoubleT(prefs->GetDouble(
+        prefs::kRestoreStartupURLsMigrated));
+    base::Time now = base::Time::Now();
+    prefs->SetDouble(prefs::kRestoreStartupURLsMigrated, now.ToDoubleT());
+    DCHECK(now > last_migration_time);
+    HISTOGRAM_CUSTOM_TIMES("Settings.StartupURLsResetTime",
+                           now - last_migration_time,

[robertshield, 2013/10/04 15:16:15]

in theory, this could be negative. What's the effect on the uma metric when that
happens?

[MAD, 2013/10/04 19:31:22]

I just tried it and it would go in the 0 bucket (if the UMA server reacts like
chrome://histograms).

If you prefer we could also make it explicit, e.g., now > last_migration_time ?
now - last_migration_time : 0

+                           base::TimeDelta::FromDays(0),
+                           base::TimeDelta::FromDays(7),
+                           50);
+    UMA_HISTOGRAM_ENUMERATION(
+        "Settings.StartupURLsMigration",
+        STARTUP_URLS_MIGRATION_METRICS_RESET,
+        STARTUP_URLS_MIGRATION_METRICS_MAX);
+  }
+
   if (!prefs->GetBoolean(prefs::kRestoreOnStartupMigrated)) {
-    // Read existing values
+    // Read existing values.
     const base::Value* homepage_is_new_tab_page_value =
         prefs->GetUserPrefValue(prefs::kHomePageIsNewTabPage);
     bool homepage_is_new_tab_page = true;