Cleanup return values in chrome/common/extensions

chrome/common/extensions/manifest_handlers/mime_types_handler.h

Index: chrome/common/extensions/manifest_handlers/mime_types_handler.h
diff --git a/chrome/common/extensions/manifest_handlers/mime_types_handler.h b/chrome/common/extensions/manifest_handlers/mime_types_handler.h
index 0ee47ccbe3fe5985a51dfed56a7a943094b82210..69a0a5da39a882eaae7d87019552759c5f59bff6 100644
--- a/chrome/common/extensions/manifest_handlers/mime_types_handler.h
+++ b/chrome/common/extensions/manifest_handlers/mime_types_handler.h
@@ -39,7 +39,7 @@ class MimeTypesHandler {
     handler_url_ = handler_url;
   }
   // The URL that will be used to handle MIME type requests.
-  const std::string handler_url() const { return handler_url_; }
+  const std::string& handler_url() const { return handler_url_; }
 
   const std::set<std::string>& mime_type_set() const { return mime_type_set_; }