fix(Offline): Fix persistent session removal (#8895)

Fixes #8882
Regression introduced in #8828

Author: tykus160

lib/drm/drm_engine.js

@@ -308,7 +308,7 @@ shaka.drm.DrmEngine = class {
    * @param {!Array<MediaKeySystemMediaCapability>} videoCapabilities
    * @return {!Promise}
    */
-  initForRemoval(keySystem, licenseServerUri, serverCertificate,
+  async initForRemoval(keySystem, licenseServerUri, serverCertificate,
       audioCapabilities, videoCapabilities) {
     const mimeTypes = [];
     if (videoCapabilities.length) {
@@ -336,6 +336,12 @@ shaka.drm.DrmEngine = class {
       const drmInfo = makeDrmInfo(audioCapabilities[0].encryptionScheme || '');
       variant.audio.drmInfos.push(drmInfo);
     }
+    // We should get the decodingInfo results for the variants after we filling
+    // in the drm infos, and before queryMediaKeys_().
+    await shaka.util.StreamUtils.getDecodingInfosForVariants([variant],
+        /* usePersistentLicenses= */ true, this.srcEquals_,
+        /* preferredKeySystems= */ []);
+    this.destroyer_.ensureNotDestroyed();
     return this.queryMediaKeys_(/* variants= */ [variant]);
   }