src: return references from getters, not copies

PR-URL: https://github.com/nodejs/node/pull/15458
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

src/node_perf.h

@@ -73,11 +73,11 @@ class PerformanceEntry : public BaseObject {
       return env_;
     }
 
-    std::string name() const {
+    const std::string& name() const {
       return name_;
     }
 
-    std::string type() const {
+    const std::string& type() const {
       return type_;
     }
 
@@ -135,11 +135,11 @@ class PerformanceEntry : public BaseObject {
 
   ~PerformanceEntry() {}
 
-  std::string name() const {
+  const std::string& name() const {
     return name_;
   }
 
-  std::string type() const {
+  const std::string& type() const {
     return type_;
   }