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

chrome/browser/protector/protector_service.cc

Index: chrome/browser/protector/protector_service.cc
diff --git a/chrome/browser/protector/protector_service.cc b/chrome/browser/protector/protector_service.cc
index b895e68190f18c20c58557f2e3ecfba52679da68..a70ec37ea3ec6b11e2009419321c5b2d28e4d4d5 100644
--- a/chrome/browser/protector/protector_service.cc
+++ b/chrome/browser/protector/protector_service.cc
@@ -119,6 +119,10 @@ ProtectedPrefsWatcher* ProtectorService::GetPrefsWatcher() {
   return prefs_watcher_.get();
 }
 
+void ProtectorService::StopWatchingPrefsForTesting() {
+  prefs_watcher_.reset();
+}
+
 ProtectorService::Item* ProtectorService::FindItemToMergeWith(
     const BaseSettingChange* change) {
   if (!change->CanBeMerged())