fix(MCap): Fix the default DRM session type w/ MCap

When there is no session type specified by a manifest parser or the
app's DRM config, we select a session type based on context (offline
or streaming).

In the EME branches of DrmEngine, we select the ultimate session type
in the engine's DrmInfo based on the configuration that was sent to
EME.  This, in turn, influences what kinds of sessions we create
later.

However, in the MediaCapabilities branch of DrmEngine, we were
defaulting to 'temporary' sessions in the engine's DrmInfo, without
regard to the input config or the load context.

This fixes the default so that it mirrors the input config to MCap.
That MCap config is not accessible at that time, so we just re-derive
the same value based on a boolean stored in DrmEngine.

In cases where there is a session type from the manifest parser (rare)
or the app's DRM config (more common), that will be preferred
regardless of context.

Change-Id: I1f408c04eff9a3006d2eddfaf748f7ab2c93cf9b

lib/media/drm_engine.js

@@ -907,7 +907,7 @@ shaka.media.DrmEngine = class {
           'We should get at least one supported MIME type');
 
       if (useMediaCapabilities) {
-        this.currentDrmInfo_ = shaka.media.DrmEngine.createDrmInfoByInfos_(
+        this.currentDrmInfo_ = this.createDrmInfoByInfos_(
             mediaKeySystemAccess.keySystem,
             drmInfosByKeySystem.get(mediaKeySystemAccess.keySystem));
       } else {
@@ -1993,7 +1993,7 @@ shaka.media.DrmEngine = class {
    *
    * @private
    */
-  static createDrmInfoByInfos_(keySystem, drmInfos) {
+  createDrmInfoByInfos_(keySystem, drmInfos) {
     /** @type {!Array.<string>} */
     const licenseServers = [];
 
@@ -2019,13 +2019,16 @@ shaka.media.DrmEngine = class {
                         'Only the first will be used.');
     }
 
+    const defaultSessionType =
+        this.usePersistentLicenses_ ? 'persistent-license' : 'temporary';
+
     /** @type {shaka.extern.DrmInfo} */
     const res = {
       keySystem,
       licenseServerUri: licenseServers[0],
       distinctiveIdentifierRequired: drmInfos[0].distinctiveIdentifierRequired,
       persistentStateRequired: drmInfos[0].persistentStateRequired,
-      sessionType: drmInfos[0].sessionType || 'temporary',
+      sessionType: drmInfos[0].sessionType || defaultSessionType,
       audioRobustness: drmInfos[0].audioRobustness || '',
       videoRobustness: drmInfos[0].videoRobustness || '',
       serverCertificate: serverCerts[0],