Cleanup: Pass std::string as const reference if possible

chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc

Index: chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc
diff --git a/chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc b/chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc
index 8fc8ff12182422058ed6eec7f42a3903522a6d79..a5e635b5f3d2f5dff72b2c41e32f627f648ecfc0 100644
--- a/chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc
+++ b/chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.cc
@@ -162,9 +162,9 @@ void NewTabPageSyncHandler::OnSigninAllowedPrefChange() {
   BuildAndSendSyncStatus();
 }
 
-void NewTabPageSyncHandler::SendSyncMessageToPage(
-    MessageType type, std::string msg,
-    std::string linktext) {
+void NewTabPageSyncHandler::SendSyncMessageToPage(MessageType type,
+                                                  const std::string& msg,
+                                                  const std::string& linktext) {
   base::DictionaryValue value;
   std::string user;
   std::string title;