fix(FairPlay): Install by default shaka.polyfill.PatchedMediaKeysAppl…

…e on older Safari versions (#8106)

docs/tutorials/fairplay.md

@@ -27,6 +27,8 @@ The support in each case would be the following:
 
 Adding FairPlay support involves a bit more work than other key systems.
 
+Note: If you are using an older version of Safari that doesn't support
+Modern EME, legacy Apple Media Keys is used by default.
 
 ## Keysystem used in EME
 

lib/polyfill/patchedmediakeys_apple.js

@@ -25,6 +25,25 @@ goog.require('shaka.util.StringUtils');
  * @export
  */
 shaka.polyfill.PatchedMediaKeysApple = class {
+  /**
+   * Installs the polyfill if needed.
+   */
+  static defaultInstall() {
+    if (!window.HTMLVideoElement || !window.WebKitMediaKeys) {
+      // No HTML5 video or no prefixed EME.
+      return;
+    }
+    if (navigator.requestMediaKeySystemAccess &&
+         // eslint-disable-next-line no-restricted-syntax
+         MediaKeySystemAccess.prototype.getConfiguration) {
+      // Unprefixed EME available
+      return;
+    }
+    // If there is no unprefixed EME and prefixed EME exists, apply installation
+    // by default. Eg: older versions of Safari.
+    shaka.polyfill.PatchedMediaKeysApple.install();
+  }
+
   /**
    * Installs the polyfill if needed.
    * @param {boolean=} enableUninstall enables uninstalling the polyfill
@@ -798,3 +817,5 @@ shaka.polyfill.PatchedMediaKeysApple.MediaKeyStatusMap = class {
  * @private {string}
  */
 shaka.polyfill.PatchedMediaKeysApple.apiName_ = 'apple';
+
+shaka.polyfill.register(shaka.polyfill.PatchedMediaKeysApple.defaultInstall);