Prefer prefixed EME on Apple devices

The unprefixed EME launched with macOS 10.14 (Mojave) rejects requests
for the key system IDs we know how to use.  So until the bug we filed
against Apple is resolved, prefer the prefixed API.

Issue #382

Change-Id: I71313be2102af2da66a6389a9e9afdebd8ae033d

lib/polyfill/patchedmediakeys_apple.js

@@ -41,11 +41,21 @@ goog.require('shaka.util.Uint8ArrayUtils');
  * Installs the polyfill if needed.
  */
 shaka.polyfill.PatchedMediaKeysApple.install = function() {
-  if (!window.HTMLVideoElement || !window.WebKitMediaKeys ||
-      (navigator.requestMediaKeySystemAccess &&
-       MediaKeySystemAccess.prototype.getConfiguration)) {
+  if (!window.HTMLVideoElement || !window.WebKitMediaKeys) {
+    // No HTML5 video or no prefixed EME.
     return;
   }
+
+  // TODO: Prefer unprefixed EME once we know how to use it.
+  // See: https://bugs.webkit.org/show_bug.cgi?id=197433
+  /*
+  if (navigator.requestMediaKeySystemAccess &&
+      MediaKeySystemAccess.prototype.getConfiguration) {
+    // Prefixed EME is preferable.
+    return;
+  }
+  */
+
   shaka.log.info('Using Apple-prefixed EME');
 
   // Alias