[api-minor] Remove the postMessageTransfers parameter, and thus the…

… ability to manually disable transferring of data, from the API

By transfering, rather than copying, `ArrayBuffer`s between the main- and worker-threads, you can avoid unnecessary allocations by only having *one* copy of the same data.
Hence manually setting `postMessageTransfers: false`, when calling `getDocument`, is a performance footgun[1] which will do nothing but waste memory.

Given that every reasonably modern browser supports `postMessage` transfers[2], I really don't see why it should be possible to force-disable this functionality.
Looking at the browser support, for `postMessage` transfers[2], it's highly unlikely that PDF.js is even usable in browsers without it. However, the feature testing of `postMessage` transfers is kept for the time being just to err on the safe side.

---
[1] This is somewhat similar to the, now removed, `disableWorker` parameter which also provided API users a much too simple way of reducing performance.

[2] See e.g. https://developer.mozilla.org/en-US/docs/Web/API/MessagePort/postMessage#Browser_compatibility and https://developer.mozilla.org/en-US/docs/Web/API/Transferable#Browser_compatibility

src/display/api.js

@@ -146,8 +146,6 @@ function setPDFNetworkStreamFactory(pdfNetworkStreamFactory) {
  * 2^16 = 65536.
  * @property {PDFWorker} worker - (optional) The worker that will be used for
  * the loading and parsing of the PDF data.
- * @property {boolean} postMessageTransfers - (optional) Enables transfer usage
- * in postMessage for ArrayBuffers. The default value is `true`.
  * @property {number} verbosity - (optional) Controls the logging level; the
  * constants from {VerbosityLevel} should be used.
  * @property {string} docBaseUrl - (optional) The base URL of the document,
@@ -319,7 +317,6 @@ function getDocument(src) {
 
  if (!worker) {
  const workerParams = {
- postMessageTransfers: params.postMessageTransfers,
  verbosity: params.verbosity,
  port: GlobalWorkerOptions.workerPort,
  };
@@ -1476,8 +1473,6 @@ class LoopbackPort {
  * @typedef {Object} PDFWorkerParameters
  * @property {string} name - (optional) The name of the worker.
  * @property {Object} port - (optional) The `workerPort`.
- * @property {boolean} postMessageTransfers - (optional) Enables transfer usage
- * in postMessage for ArrayBuffers. The default value is `true`.
  * @property {number} verbosity - (optional) Controls the logging level; the
  * constants from {VerbosityLevel} should be used.
  */
@@ -1568,15 +1563,15 @@ const PDFWorker = (function PDFWorkerClosure() {
  * @param {PDFWorkerParameters} params - The worker initialization parameters.
  */
  class PDFWorker {
- constructor({ name = null, port = null, postMessageTransfers = true,
+ constructor({ name = null, port = null,
  verbosity = getVerbosityLevel(), } = {}) {
  if (port && pdfWorkerPorts.has(port)) {
  throw new Error('Cannot use more than one PDFWorker per port');
  }
 
  this.name = name;
  this.destroyed = false;
- this.postMessageTransfers = postMessageTransfers !== false;
+ this.postMessageTransfers = true;
  this.verbosity = verbosity;
 
  this._readyCapability = createPromiseCapability();
@@ -1705,7 +1700,7 @@ const PDFWorker = (function PDFWorkerClosure() {
  try {
  messageHandler.send('test', testObj, [testObj.buffer]);
  } catch (ex) {
- info('Cannot use postMessage transfers');
+ warn('Cannot use postMessage transfers.');
  testObj[0] = 0;
  messageHandler.send('test', testObj);
  }

web/app_options.js

@@ -206,11 +206,6 @@ const defaultOptions = {
  value: false,
  kind: OptionKind.API,
  },
- postMessageTransfers: {
- /** @type {boolean} */
- value: true,
- kind: OptionKind.API,
- },
  verbosity: {
  /** @type {number} */
  value: 1,