Stop bundling the ReadableStream polyfill in MOZCENTRAL builds (PR 10470 follow-up)

Based on the discussion in https://bugzilla.mozilla.org/show_bug.cgi?id=1521413, this patch simply removes the `ReadableStream` polyfill completely from MOZCENTRAL builds.

With this patch, the size of the `gulp mozcentral` build target is thus further reduced (building on PR 10470):

|       | `build/mozcentral`
|-------|-------------------
|master |   3 339 666
|patch  |   3 209 572

extensions/firefox/content/streams_polyfill.js

@@ -1,19 +0,0 @@
-/* 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.
- */
-
-if (typeof ReadableStream === "undefined") {
-  require("../../../src/shared/global_scope").ReadableStream =
-    require("../../../external/streams/streams-lib").ReadableStream;
-}

gulpfile.js

@@ -766,16 +766,6 @@ function preprocessDefaultPreferences(content) {
           content + '\n');
 }
 
-function createMozcentralStreamsPolyfillBundle(defines) {
-  var streamsPolyfillOutputName = 'streams_polyfill.js';
-
-  var streamsPolyfillFileConfig = createWebpackConfig(defines, {
-    filename: streamsPolyfillOutputName,
-  });
-  return gulp.src('./extensions/firefox/content/streams_polyfill.js')
-             .pipe(webpack2Stream(streamsPolyfillFileConfig));
-}
-
 gulp.task('mozcentral-pre', gulp.series('buildnumber', 'locale', function () {
   console.log();
   console.log('### Building mozilla-central extension');
@@ -797,8 +787,6 @@ gulp.task('mozcentral-pre', gulp.series('buildnumber', 'locale', function () {
   return merge([
     createBundle(defines).pipe(gulp.dest(MOZCENTRAL_CONTENT_DIR + 'build')),
     createWebBundle(defines).pipe(gulp.dest(MOZCENTRAL_CONTENT_DIR + 'web')),
-    createMozcentralStreamsPolyfillBundle(defines)
-        .pipe(gulp.dest(MOZCENTRAL_CONTENT_DIR + 'build')),
     gulp.src(COMMON_WEB_FILES, { base: 'web/', })
         .pipe(gulp.dest(MOZCENTRAL_CONTENT_DIR + 'web')),
     gulp.src(['external/bcmaps/*.bcmap', 'external/bcmaps/LICENSE'],

src/pdf.worker.js

@@ -12,14 +12,10 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-/* eslint-disable no-restricted-globals, no-unused-vars */
+/* eslint-disable no-unused-vars */
 
 'use strict';
 
-if (PDFJSDev.test('MOZCENTRAL') && typeof ReadableStream === 'undefined') {
-  importScripts('./streams_polyfill.js');
-}
-
 const pdfjsVersion = PDFJSDev.eval('BUNDLE_VERSION');
 const pdfjsBuild = PDFJSDev.eval('BUNDLE_BUILD');
 

src/shared/streams_polyfill.js

@@ -15,10 +15,10 @@
 /* eslint-disable no-restricted-globals */
 
 if (typeof PDFJSDev !== 'undefined' && PDFJSDev.test('MOZCENTRAL')) {
-  // On the main-thread the `streams_polyfill.js` file is loaded using a
+  if (typeof ReadableStream === 'undefined') {
-  // <script> tag; see `web/viewer-snippet-firefox-extension.html`.
+    throw new Error('Please enable ReadableStream support by resetting the ' +
-  // On the worker-thread the `streams_polyfill.js` file is (conditionally)
+      '"javascript.options.streams" preference to "true" in about:config.');
-  // loaded using `importScripts`; see `src/pdf.worker.js`.
+  }
   exports.ReadableStream = ReadableStream;
 } else {
   let isReadableStreamSupported = false;

web/viewer-snippet-firefox-extension.html

@@ -1,10 +1,3 @@
 <!-- This snippet is used in the Firefox extension (included from viewer.html) -->
 <base href="resource://pdf.js/web/">
-<script>
-  (function() {
-    if (typeof ReadableStream === "undefined") {
-      document.write("<script src=\"../build/streams_polyfill.js\"><\/script>");
-    }
-  })();
-</script>
 <script src="../build/pdf.js"></script>