Use LoopbackPort in the "message_handler" unit-tests

There's no good reason, as far as I can tell, to duplicate the functionality of the `LoopbackPort` in the unit-tests. The only difference between the implementations is that `LoopbackPort` mimics the (native) structured cloning, however that shouldn't matter here since the tests are only sending "simple" data (strings respectively arrays with numbers).

Furthermore the patch also changes `LoopbackPort` to default to using "structured cloning" and deferred invocation of the listeners, since native typed array support is now a requirement for using the PDF.js library.

src/display/api.js

@@ -1205,7 +1205,7 @@ var PDFPageProxy = (function PDFPageProxyClosure() {
 })();
 
 class LoopbackPort {
-  constructor(defer) {
+  constructor(defer = true) {
     this._listeners = [];
     this._defer = defer;
     this._deferred = Promise.resolve(undefined);

test/unit/message_handler_spec.js

@@ -14,39 +14,10 @@
  */
 
 import { createPromiseCapability } from '../../src/shared/util';
+import { LoopbackPort } from '../../src/display/api';
 import { MessageHandler } from '../../src/shared/message_handler';
 
 describe('message_handler', function () {
-  // Temporary fake port for sending messages between main and worker.
-  class FakePort {
-    constructor() {
-      this._listeners = [];
-      this._deferred = Promise.resolve(undefined);
-    }
-
-    postMessage(obj) {
-      let event = { data: obj, };
-      this._deferred.then(() => {
-        this._listeners.forEach(function (listener) {
-          listener.call(this, event);
-        }, this);
-      });
-    }
-
-    addEventListener(name, listener) {
-      this._listeners.push(listener);
-    }
-
-    removeEventListener(name, listener) {
-      let i = this._listeners.indexOf(listener);
-      this._listeners.splice(i, 1);
-    }
-
-    terminate() {
-      this._listeners = [];
-    }
-  }
-
   // Sleep function to wait for sometime, similar to setTimeout but faster.
   function sleep(ticks) {
     return Promise.resolve().then(() => {
@@ -56,7 +27,7 @@ describe('message_handler', function () {
 
   describe('sendWithStream', function () {
     it('should return a ReadableStream', function () {
-      let port = new FakePort();
+      let port = new LoopbackPort();
       let messageHandler1 = new MessageHandler('main', 'worker', port);
       let readable = messageHandler1.sendWithStream('fakeHandler');
       // Check if readable is an instance of ReadableStream.
@@ -66,7 +37,7 @@ describe('message_handler', function () {
 
     it('should read using a reader', function (done) {
       let log = '';
-      let port = new FakePort();
+      let port = new LoopbackPort();
       let messageHandler1 = new MessageHandler('main', 'worker', port);
       let messageHandler2 = new MessageHandler('worker', 'main', port);
       messageHandler2.on('fakeHandler', (data, sink) => {
@@ -110,7 +81,7 @@ describe('message_handler', function () {
 
     it('should not read any data when cancelled', function (done) {
       let log = '';
-      let port = new FakePort();
+      let port = new LoopbackPort();
       let messageHandler2 = new MessageHandler('worker', 'main', port);
       messageHandler2.on('fakeHandler', (data, sink) => {
         sink.onPull = function () {
@@ -162,7 +133,7 @@ describe('message_handler', function () {
 
     it('should not read when errored', function(done) {
       let log = '';
-      let port = new FakePort();
+      let port = new LoopbackPort();
       let messageHandler2 = new MessageHandler('worker', 'main', port);
       messageHandler2.on('fakeHandler', (data, sink) => {
         sink.onPull = function () {
@@ -205,7 +176,7 @@ describe('message_handler', function () {
 
     it('should read data with blocking promise', function (done) {
       let log = '';
-      let port = new FakePort();
+      let port = new LoopbackPort();
       let messageHandler2 = new MessageHandler('worker', 'main', port);
       messageHandler2.on('fakeHandler', (data, sink) => {
         sink.onPull = function () {
@@ -266,7 +237,7 @@ describe('message_handler', function () {
     it('should read data with blocking promise and buffer whole data' +
        ' into stream', function (done) {
       let log = '';
-      let port = new FakePort();
+      let port = new LoopbackPort();
       let messageHandler2 = new MessageHandler('worker', 'main', port);
       messageHandler2.on('fakeHandler', (data, sink) => {
         sink.onPull = function () {
@@ -326,7 +297,7 @@ describe('message_handler', function () {
 
     it('should ignore any pull after close is called', function (done) {
       let log = '';
-      let port = new FakePort();
+      let port = new LoopbackPort();
       let capability = createPromiseCapability();
       let messageHandler2 = new MessageHandler('worker', 'main', port);
       messageHandler2.on('fakeHandler', (data, sink) => {