Fix exception thrown for Chrome & Firefox on iOS

Because we have some polyfills and blacklists that are specific to
Safari and iOS, we need to detect specific versions of Safari and iOS.
The existing detection of Safari/iOS versions was in multiple places,
and did not account for non-Safari browsers on iOS.  This refactor
allows us to correctly detect iOS Chrome, and fixes a fatal exception
thrown in the MediaSource polyfill for all non-Safari browsers on iOS.

Change-Id: Ic88dc1a4c82087054cd4791dbf295b7ea2aeab09

lib/player.js

@@ -708,13 +708,11 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
       return false;
     }
 
-    // We do not support iOS 9, 10, or 11.
-    if (shaka.util.Platform.isApple() && shaka.util.Platform.isMobile()) {
-      const match = navigator.appVersion.match(/Version\/(\d+)/);
-      const version = parseInt(match[1], /* base= */ 10);
-      if (version < 12) {
-        return false;
-      }
+    // We do not support iOS 9, 10, or 11, nor those same versions of desktop
+    // Safari.
+    const safariVersion = shaka.util.Platform.safariVersion();
+    if (safariVersion && safariVersion < 12) {
+      return false;
     }
 
     // DRM support is not strictly necessary, but the APIs at least need to be

lib/polyfill/mediasource.js

@@ -25,6 +25,7 @@ shaka.polyfill.MediaSource = class {
     // example, and instances are only accessible after setting up MediaSource
     // on a video element.  Because of this, we use UA detection and other
     // platform detection tricks to decide which patches to install.
+    const safariVersion = shaka.util.Platform.safariVersion();
 
     if (!window.MediaSource) {
       shaka.log.info('No MSE implementation available.');
@@ -33,27 +34,13 @@ shaka.polyfill.MediaSource = class {
       shaka.log.info('Patching Chromecast MSE bugs.');
       // Chromecast cannot make accurate determinations via isTypeSupported.
       shaka.polyfill.MediaSource.patchCastIsTypeSupported_();
-    } else if (shaka.util.Platform.isApple()) {
-      const match = navigator.appVersion.match(/Version\/(\d+)/);
-      const version = parseInt(match[1], /* base= */ 10);
-
+    } else if (safariVersion) {
       // TS content is broken on Safari in general.
       // See https://github.com/google/shaka-player/issues/743
       // and https://bugs.webkit.org/show_bug.cgi?id=165342
       shaka.polyfill.MediaSource.rejectTsContent_();
 
-      if (version <= 10) {
-        // Safari 8 does not implement appendWindowEnd.
-        // Safari 9 & 10 do not correctly implement abort() on SourceBuffer.
-        // Bug filed: https://bugs.webkit.org/show_bug.cgi?id=160316
-        // Bug filed: https://bugs.webkit.org/show_bug.cgi?id=165342
-        // Safari 10 fires spurious 'updateend' events after endOfStream().
-        // Bug filed: https://bugs.webkit.org/show_bug.cgi?id=165336
-
-        // Blacklist these very outdated versions.
-        shaka.log.info('Blacklisting MSE on Safari <= 10.');
-        shaka.polyfill.MediaSource.blacklist_();
-      } else if (version <= 12) {
+      if (safariVersion <= 12) {
         shaka.log.info('Patching Safari 11 & 12 MSE bugs.');
         // Safari 11 & 12 do not correctly implement abort() on SourceBuffer.
         // Calling abort() before appending a segment causes that segment to be
@@ -85,17 +72,6 @@ shaka.polyfill.MediaSource = class {
     }
   }
 
-  /**
-   * Blacklist the current browser by removing media source. A side-effect of
-   * this will be to make |shaka.util.Platform.supportsMediaSource| return
-   * |false|.
-   *
-   * @private
-   */
-  static blacklist_() {
-    window['MediaSource'] = null;
-  }
-
   /**
    * Stub out abort().  On some buggy MSE implementations, calling abort()
    * causes various problems.

lib/util/platform.js

@@ -116,14 +116,56 @@ shaka.util.Platform = class {
 
 
   /**
-   * Check if the current platform is an Apple device (iOS, desktop Safari, etc)
+   * Check if the current platform is from Apple.
+   *
+   * Returns true on all iOS browsers and on desktop Safari.
+   *
+   * Returns false for non-Safari browsers on macOS, which are independent of
+   * Apple.
    *
    * @return {boolean}
    */
   static isApple() {
     return !!navigator.vendor && navigator.vendor.includes('Apple');
   }
 
+  /**
+   * Returns a major version number for Safari, or Safari-based iOS browsers.
+   *
+   * For example:
+   *   - Safari 13.0.4 on macOS returns 13.
+   *   - Safari on iOS 13.3.1 returns 13.
+   *   - Chrome on iOS 13.3.1 returns 13 (since this is based on Safari/WebKit).
+   *   - Chrome on macOS returns null (since this is independent of Apple).
+   *
+   * Returns null on Firefox on iOS, where this version information is not
+   * available.
+   *
+   * @return {?number} A major version number or null if not iOS.
+   */
+  static safariVersion() {
+    // All iOS browsers and desktop Safari will return true for isApple().
+    if (!shaka.util.Platform.isApple()) {
+      return null;
+    }
+
+    // This works for iOS Safari and desktop Safari, which contain something
+    // like "Version/13.0" indicating the major Safari or iOS version.
+    let match = navigator.userAgent.match(/Version\/(\d+)/);
+    if (match) {
+      return parseInt(match[1], /* base= */ 10);
+    }
+
+    // This works for all other browsers on iOS, which contain something like
+    // "OS 13_3" indicating the major & minor iOS version.
+    match = navigator.userAgent.match(/OS (\d+)(?:_\d+)?/);
+    if (match) {
+      return parseInt(match[1], /* base= */ 10);
+    }
+
+    return null;
+  }
+
   /**
    * Guesses if the platform is a mobile one (iOS or Android).
    *