Add flag to track migration from email to gaia id.

chrome/browser/signin/account_tracker_service_factory.cc

Index: chrome/browser/signin/account_tracker_service_factory.cc
diff --git a/chrome/browser/signin/account_tracker_service_factory.cc b/chrome/browser/signin/account_tracker_service_factory.cc
index 12964277b36926c0629502e1aa124acfe06ec9e7..186983487d9c0abb2f526a1f4388344be3a2c510 100644
--- a/chrome/browser/signin/account_tracker_service_factory.cc
+++ b/chrome/browser/signin/account_tracker_service_factory.cc
@@ -11,6 +11,7 @@
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "components/signin/core/browser/account_tracker_service.h"
 #include "components/signin/core/browser/profile_oauth2_token_service.h"
+#include "components/signin/core/common/signin_pref_names.h"
 
 AccountTrackerServiceFactory::AccountTrackerServiceFactory()
     : BrowserContextKeyedServiceFactory(
@@ -39,6 +40,10 @@ void AccountTrackerServiceFactory::RegisterProfilePrefs(
   registry->RegisterListPref(
       AccountTrackerService::kAccountInfoPref,
       user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
+  registry->RegisterIntegerPref(
+      prefs::kAccountIdMigrationState,
+      AccountTrackerService::MIGRATION_NOT_STARTED,
+      user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
 }
 
 KeyedService* AccountTrackerServiceFactory::BuildServiceInstanceFor(