fix(cast): Fix Shaka+Cast apps using IndexedDB

The IndexedDB polyfill was preventing Cast apps from using IndexedDB
outside of Shaka Player.  Instead of breaking IDB, we should just
directly disallow offline storage on the Cast platform.

Fixes #2850

b/168565999

Change-Id: Ie504531c412723cc0f93530b2e34000873bfaf32

build/types/polyfill

@@ -3,7 +3,6 @@
 +../../node_modules/eme-encryption-scheme-polyfill/index.js
 +../../lib/polyfill/encryption_scheme.js
 +../../lib/polyfill/fullscreen.js
-+../../lib/polyfill/indexed_db.js
 +../../lib/polyfill/input_event.js
 +../../lib/polyfill/languages.js
 +../../lib/polyfill/mathround.js

lib/offline/indexeddb/storage_mechanism.js

@@ -366,7 +366,13 @@ shaka.offline.indexeddb.StorageMechanism.SESSION_ID_STORE = 'session-ids';
 shaka.offline.StorageMuxer.register(
     'idb',
     () => {
-      return window.indexedDB ?
-              new shaka.offline.indexeddb.StorageMechanism() :
-              null;
+      // Offline storage is not supported on the Chromecast platform.
+      if (shaka.util.Platform.isChromecast()) {
+        return null;
+      }
+      // Offline storage requires the IndexedDB API.
+      if (!window.indexedDB) {
+        return null;
+      }
+      return new shaka.offline.indexeddb.StorageMechanism();
     });

shaka-player.uncompiled.js

@@ -34,7 +34,6 @@ goog.require('shaka.offline.Storage');
 goog.require('shaka.offline.indexeddb.StorageMechanism');
 goog.require('shaka.polyfill.EncryptionScheme');
 goog.require('shaka.polyfill.Fullscreen');
-goog.require('shaka.polyfill.IndexedDB');
 goog.require('shaka.polyfill.InputEvent');
 goog.require('shaka.polyfill.MathRound');
 goog.require('shaka.polyfill.MediaSource');