[Password Manager] Add UMA stats for custom passphrase users.

chrome/browser/password_manager/mock_password_store_service.cc

Index: chrome/browser/password_manager/mock_password_store_service.cc
diff --git a/chrome/browser/password_manager/mock_password_store_service.cc b/chrome/browser/password_manager/mock_password_store_service.cc
index 7ad2f2497ccd8f5db26a4fa01afa39bf869e98c3..b1eec9eb7b621e0ba68036112fe8e82bdb041bcb 100644
--- a/chrome/browser/password_manager/mock_password_store_service.cc
+++ b/chrome/browser/password_manager/mock_password_store_service.cc
@@ -12,7 +12,7 @@ KeyedService* MockPasswordStoreService::Build(
   scoped_refptr<password_manager::PasswordStore> store(
       new password_manager::MockPasswordStore);
   if (!store.get() ||
-      !store->Init(syncer::SyncableService::StartSyncFlare(), ""))
+      !store->Init(syncer::SyncableService::StartSyncFlare()))
     return NULL;
   return new MockPasswordStoreService(store);
 }