add a separate class for HotUpdateChunk

lib/HotUpdateChunk.js

@@ -0,0 +1,16 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+"use strict";
+
+const Chunk = require("./Chunk");
+
+class HotUpdateChunk extends Chunk {
+	constructor() {
+		super();
+		this.removedModules = undefined;
+	}
+}
+
+module.exports = HotUpdateChunk;

lib/HotUpdateChunkTemplate.js

@@ -5,7 +5,7 @@
 "use strict";
 
 const Template = require("./Template");
-const Chunk = require("./Chunk");
+const HotUpdateChunk = require("./HotUpdateChunk");
 const { Tapable, SyncWaterfallHook, SyncHook } = require("tapable");
 
 module.exports = class HotUpdateChunkTemplate extends Tapable {
@@ -41,7 +41,7 @@ module.exports = class HotUpdateChunkTemplate extends Tapable {
 		moduleTemplate,
 		dependencyTemplates
 	) {
-		const hotUpdateChunk = new Chunk();
+		const hotUpdateChunk = new HotUpdateChunk();
 		hotUpdateChunk.id = id;
 		hotUpdateChunk.setModules(modules);
 		hotUpdateChunk.removedModules = removedModules;