child_process: move anonymous class to top level

Move the anonymous class out of setupChannel to clarify code.

PR-URL: #11147
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

Author: JacksonTian

lib/internal/child_process.js

@@ -407,6 +407,24 @@ ChildProcess.prototype.unref = function() {
   if (this._handle) this._handle.unref();
 };
 
+class Control extends EventEmitter {
+  constructor(channel) {
+    super();
+    this.channel = channel;
+    this.refs = 0;
+  }
+  ref() {
+    if (++this.refs === 1) {
+      this.channel.ref();
+    }
+  }
+  unref() {
+    if (--this.refs === 0) {
+      this.channel.unref();
+      this.emit('unref');
+    }
+  }
+}
 
 function setupChannel(target, channel) {
   target.channel = channel;
@@ -421,24 +439,7 @@ function setupChannel(target, channel) {
   target._handleQueue = null;
   target._pendingHandle = null;
 
-  const control = new class extends EventEmitter {
-    constructor() {
-      super();
-      this.channel = channel;
-      this.refs = 0;
-    }
-    ref() {
-      if (++this.refs === 1) {
-        this.channel.ref();
-      }
-    }
-    unref() {
-      if (--this.refs === 0) {
-        this.channel.unref();
-        this.emit('unref');
-      }
-    }
-  }();
+  const control = new Control(channel);
 
   var decoder = new StringDecoder('utf8');
   var jsonBuffer = '';