[Password Manager] Add UMA stats to track interaction with synced accounts.

chrome/browser/password_manager/password_store_mac.cc

Index: chrome/browser/password_manager/password_store_mac.cc
diff --git a/chrome/browser/password_manager/password_store_mac.cc b/chrome/browser/password_manager/password_store_mac.cc
index 1cfe8fa03b103f70929c594d1cb5d60ec75f586e..88a30e56bfa9adae6d67b2f3782785438236c59b 100644
--- a/chrome/browser/password_manager/password_store_mac.cc
+++ b/chrome/browser/password_manager/password_store_mac.cc
@@ -868,8 +868,8 @@ PasswordStoreMac::GetBackgroundTaskRunner() {
   return (thread_.get()) ? thread_->message_loop_proxy() : NULL;
 }
 
-void PasswordStoreMac::ReportMetricsImpl() {
-  login_metadata_db_->ReportMetrics();
+void PasswordStoreMac::ReportMetricsImpl(const std::string& sync_username) {
+  login_metadata_db_->ReportMetrics(sync_username);
 }
 
 PasswordStoreChangeList PasswordStoreMac::AddLoginImpl(