[protector] Bump Preferences backup version to 3 to mitigate the startup prefs migration.

chrome/browser/protector/protected_prefs_watcher.cc

Index: chrome/browser/protector/protected_prefs_watcher.cc
diff --git a/chrome/browser/protector/protected_prefs_watcher.cc b/chrome/browser/protector/protected_prefs_watcher.cc
index 1f991769cce77e1ebfeffcc76e940113d193a02f..5f98e153f9c0fea0224de24455d2d9d36aeebca3 100644
--- a/chrome/browser/protector/protected_prefs_watcher.cc
+++ b/chrome/browser/protector/protected_prefs_watcher.cc
@@ -63,7 +63,7 @@ void StringAppendStringDictionary(const base::DictionaryValue* dict,
 }  // namespace
 
 // static
-const int ProtectedPrefsWatcher::kCurrentVersionNumber = 2;
+const int ProtectedPrefsWatcher::kCurrentVersionNumber = 3;
 
 ProtectedPrefsWatcher::ProtectedPrefsWatcher(Profile* profile)
     : is_backup_valid_(true),
@@ -208,8 +208,18 @@ void ProtectedPrefsWatcher::MigrateOldBackupIfNeeded() {
 
   switch (current_version) {
     case 1:
+      // Add pinned tabs.
       prefs->Set(kBackupPinnedTabs, *prefs->GetList(prefs::kPinnedTabs));
       // FALL THROUGH
+
+    case 2:
+      // SessionStartupPref migration.
+      DCHECK(prefs->GetBoolean(prefs::kRestoreOnStartupMigrated));
+      prefs->SetInteger(kBackupRestoreOnStartup,
+                        prefs->GetInteger(prefs::kRestoreOnStartup));
+      prefs->Set(kBackupURLsToRestoreOnStartup,
+                 *prefs->GetList(prefs::kURLsToRestoreOnStartup));
+      // FALL THROUGH
   }
 
   prefs->SetInteger(kBackupVersion, kCurrentVersionNumber);