perf_hooks: use for...of

PR-URL: #31049
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/perf_hooks.js

@@ -320,12 +320,11 @@ class PerformanceObserver extends AsyncResource {
   disconnect() {
     const observerCountsGC = observerCounts[NODE_PERFORMANCE_ENTRY_TYPE_GC];
     const types = this[kTypes];
-    const keys = ObjectKeys(types);
-    for (var n = 0; n < keys.length; n++) {
-      const item = types[keys[n]];
+    for (const key of ObjectKeys(types)) {
+      const item = types[key];
       if (item) {
         L.remove(item);
-        observerCounts[keys[n]]--;
+        observerCounts[key]--;
       }
     }
     this[kTypes] = {};
@@ -351,8 +350,7 @@ class PerformanceObserver extends AsyncResource {
     this[kBuffer][kEntries] = [];
     L.init(this[kBuffer][kEntries]);
     this[kBuffering] = Boolean(options.buffered);
-    for (var n = 0; n < entryTypes.length; n++) {
-      const entryType = entryTypes[n];
+    for (const entryType of entryTypes) {
       const list = getObserversList(entryType);
       if (this[kTypes][entryType]) continue;
       const item = { obs: this };