Introduce a GlobalWorkerOptions object for (basic) Worker configuration

Compared to most other options currently/previously residing on the global `PDFJS` object, some of the Worker specific ones (e.g. `workerPort`/`workerSrc`) probably cannot be moved into options provided directly when initializing e.g. `PDFWorker`.
The reason is that in some cases, e.g. the Webpack examples, we try to provide Worker auto-configuration and I cannot see a good solution for that use-case if we completely remove the globally available Worker configuration.

However inline with previous patches for PDF.js version `2.0`, it does seem like a worthwhile goal to move away from storing options directly on the global `PDFJS` object, since that is a pattern we should avoid going forward. Especially since one of the (eventual) goals is to attempt to *completely* remove the global `PDFJS` object, and rely solely on exporting/importing the needed functionality.

By introducing the `GlobalWorkerOptions` we thus have larger flexibility in the future, if/when the global `PDFJS` object will be removed.

Author: Snuffleupagus

src/display/global.js

@@ -26,6 +26,7 @@ import {
 } from './api';
 import { AnnotationLayer } from './annotation_layer';
 import globalScope from '../shared/global_scope';
+import { GlobalWorkerOptions } from './worker_options';
 import { Metadata } from './metadata';
 import { renderTextLayer } from './text_layer';
 import { SVGGraphics } from './svg';
@@ -208,6 +209,7 @@ PDFJS.getDocument = getDocument;
 PDFJS.LoopbackPort = LoopbackPort;
 PDFJS.PDFDataRangeTransport = PDFDataRangeTransport;
 PDFJS.PDFWorker = PDFWorker;
+PDFJS.GlobalWorkerOptions = GlobalWorkerOptions;
 
 PDFJS.getFilenameFromUrl = getFilenameFromUrl;
 

src/display/worker_options.js

@@ -0,0 +1,39 @@
+/* Copyright 2018 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const GlobalWorkerOptions = Object.create(null);
+
+/**
+ * Defines global port for worker process. Overrides the `workerSrc` option.
+ * @var {Object}
+ */
+GlobalWorkerOptions.workerPort = (GlobalWorkerOptions.workerPort === undefined ?
+                                  null : GlobalWorkerOptions.workerPort);
+
+/**
+ * Path and filename of the worker file. Required when workers are enabled in
+ * development mode. If unspecified in production builds, the worker will be
+ * loaded based on the location of the `pdf.js` file.
+ *
+ * NOTE: The `workerSrc` should always be set in custom applications, in order
+ *       to prevent issues caused by third-party frameworks and libraries.
+ * @var {string}
+ */
+GlobalWorkerOptions.workerSrc = (GlobalWorkerOptions.workerSrc === undefined ?
+                                 '' : GlobalWorkerOptions.workerSrc);
+
+export {
+  GlobalWorkerOptions,
+};

src/pdf.js

@@ -28,6 +28,7 @@ var pdfjsDisplayTextLayer = require('./display/text_layer.js');
 var pdfjsDisplayAnnotationLayer = require('./display/annotation_layer.js');
 var pdfjsDisplayDOMUtils = require('./display/dom_utils.js');
 var pdfjsDisplaySVG = require('./display/svg.js');
+let pdfjsDisplayWorkerOptions = require('./display/worker_options.js');
 
 if (typeof PDFJSDev === 'undefined' || PDFJSDev.test('GENERIC')) {
   const isNodeJS = require('./shared/is_node.js');
@@ -93,3 +94,4 @@ exports.RenderingCancelledException =
 exports.getFilenameFromUrl = pdfjsDisplayDOMUtils.getFilenameFromUrl;
 exports.LinkTarget = pdfjsDisplayDOMUtils.LinkTarget;
 exports.addLinkAttributes = pdfjsDisplayDOMUtils.addLinkAttributes;
+exports.GlobalWorkerOptions = pdfjsDisplayWorkerOptions.GlobalWorkerOptions;