fix(@angular-devkit/build-angular): addresses issue were deployUrl has no effect with serve

Closes #11952

Author: alan-agius4

packages/angular_devkit/build_angular/src/dev-server/index.ts

@@ -55,6 +55,7 @@ export interface DevServerBuilderOptions {
   vendorChunk?: boolean;
   commonChunk?: boolean;
   baseHref?: string;
+  deployUrl?: string;
   progress?: boolean;
   poll?: number;
   verbose?: boolean;
@@ -333,7 +334,7 @@ export class DevServerBuilder implements Builder<DevServerBuilderOptions> {
     let servePath = options.servePath;
     if (!servePath && servePath !== '') {
       const defaultServePath =
-        this._findDefaultServePath(browserOptions.baseHref, browserOptions.deployUrl);
+        this._findDefaultServePath(browserOptions.baseHref, options.deployUrl);
       const showWarning = options.servePathDefaultWarning;
       if (defaultServePath == null && showWarning) {
         this.context.logger.warn(tags.oneLine`

packages/angular_devkit/build_angular/test/dev-server/deploy-url_spec_large.ts

@@ -0,0 +1,30 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import { request, runTargetSpec } from '@angular-devkit/architect/testing';
+import { from } from 'rxjs';
+import { concatMap, take, tap } from 'rxjs/operators';
+import { DevServerBuilderOptions } from '../../src';
+import { devServerTargetSpec, host } from '../utils';
+
+
+describe('Dev Server Deploy Url', () => {
+  beforeEach(done => host.initialize().toPromise().then(done, done.fail));
+  afterEach(done => host.restore().toPromise().then(done, done.fail));
+
+  it('works', (done) => {
+    const overrides: Partial<DevServerBuilderOptions> = { deployUrl: 'test/' };
+
+    runTargetSpec(host, devServerTargetSpec, overrides).pipe(
+      tap((buildEvent) => expect(buildEvent.success).toBe(true)),
+      concatMap(() => from(request('http://localhost:4200/test/polyfills.js'))),
+      tap(response => expect(response).toContain('window["webpackJsonp"]')),
+      take(1),
+    ).toPromise().then(done, done.fail);
+  }, 30000);
+});