Implement robustness strings in requestMediaKeySystemAccess().

media/test/data/eme_player_js/player_utils.js

Index: media/test/data/eme_player_js/player_utils.js
diff --git a/media/test/data/eme_player_js/player_utils.js b/media/test/data/eme_player_js/player_utils.js
index d72bef7aa630e73a1596fb24ccee7da197160e8c..86a3e0efd8258bb9a95c44f1c7516cd2e4a2d6bd 100644
--- a/media/test/data/eme_player_js/player_utils.js
+++ b/media/test/data/eme_player_js/player_utils.js
@@ -85,8 +85,10 @@ PlayerUtils.registerEMEEventListeners = function(player) {
 
   this.registerDefaultEventListeners(player);
   Utils.timeLog('Setting video media keys: ' + player.testConfig.keySystem);
+  var persistentState = player.testConfig.sessionToLoad ? "required"
+                                                        : "optional";
   return navigator.requestMediaKeySystemAccess(
-      player.testConfig.keySystem, [{}])
+      player.testConfig.keySystem, [{persistentState: persistentState}])
       .then(function(access) { return access.createMediaKeys(); })
       .then(function(mediaKeys) {
         return player.video.setMediaKeys(mediaKeys);