Remove year+ old migration support of "session.urls_to_restore_on_startup".

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 3af7469fbdc2037b28fa38d89b62169a4191051e..de05923b5a1c7d4b02c4901a0307e1ea22987a1c 100644
--- a/chrome/browser/prefs/session_startup_pref.cc
+++ b/chrome/browser/prefs/session_startup_pref.cc
@@ -66,9 +66,7 @@ void SessionStartupPref::RegisterProfilePrefs(
       user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
   registry->RegisterListPref(prefs::kURLsToRestoreOnStartup,
                              user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
-  registry->RegisterListPref(prefs::kURLsToRestoreOnStartupOld);
   registry->RegisterBooleanPref(prefs::kRestoreOnStartupMigrated, false);
-  registry->RegisterInt64Pref(prefs::kRestoreStartupURLsMigrationTime, false);
 }
 
 // static
@@ -138,55 +136,6 @@ SessionStartupPref SessionStartupPref::GetStartupPref(PrefService* prefs) {
 // static
 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.
-  StartupURLsMigrationMetrics metrics_result =
-      STARTUP_URLS_MIGRATION_METRICS_MAX;
-  const base::ListValue* old_startup_urls =
-      prefs->GetList(prefs::kURLsToRestoreOnStartupOld);
-  if (!prefs->GetUserPrefValue(prefs::kRestoreStartupURLsMigrationTime)) {
-    // Record the absence of the migration timestamp, this will get overwritten
-    // below if migration occurs now.
-    metrics_result = STARTUP_URLS_MIGRATION_METRICS_NOT_PRESENT;
-
-    // Seems like we never migrated, do it if necessary.
-    if (!prefs->GetUserPrefValue(prefs::kURLsToRestoreOnStartup)) {
-      if (old_startup_urls && !old_startup_urls->empty()) {
-        prefs->Set(prefs::kURLsToRestoreOnStartup, *old_startup_urls);
-        prefs->ClearPref(prefs::kURLsToRestoreOnStartupOld);
-      }
-      metrics_result = STARTUP_URLS_MIGRATION_METRICS_PERFORMED;
-    }
-
-    prefs->SetInt64(prefs::kRestoreStartupURLsMigrationTime,
-                    base::Time::Now().ToInternalValue());
-  } else if (old_startup_urls && !old_startup_urls->empty()) {
-    // Migration needs to be reset.
-    prefs->ClearPref(prefs::kURLsToRestoreOnStartupOld);
-    base::Time last_migration_time = base::Time::FromInternalValue(
-        prefs->GetInt64(prefs::kRestoreStartupURLsMigrationTime));
-    base::Time now = base::Time::Now();

[gab, 2015/08/24 21:48:45]

Cross-referencing with https://codereview.chromium.org/24930003 which introduced
this code, looks like time.h and histograms.h were added then and that this was
still there only use in this file to this day so they can be removed.

[sdefresne, 2015/08/25 08:36:10]

Done.

-    prefs->SetInt64(prefs::kRestoreStartupURLsMigrationTime,
-                    now.ToInternalValue());
-    if (now < last_migration_time)
-      last_migration_time = now;
-    UMA_HISTOGRAM_CUSTOM_TIMES("Settings.StartupURLsResetTime",
-                               now - last_migration_time,
-                               base::TimeDelta::FromDays(0),
-                               base::TimeDelta::FromDays(7),
-                               50);
-    metrics_result = STARTUP_URLS_MIGRATION_METRICS_RESET;
-  }
-
-  // Record a metric migration event if something interesting happened.
-  if (metrics_result != STARTUP_URLS_MIGRATION_METRICS_MAX) {
-    UMA_HISTOGRAM_ENUMERATION(
-          "Settings.StartupURLsMigration",
-          metrics_result,
-          STARTUP_URLS_MIGRATION_METRICS_MAX);
-  }
-
   if (!prefs->GetBoolean(prefs::kRestoreOnStartupMigrated)) {
     // Read existing values.
     const base::Value* homepage_is_new_tab_page_value =