Implement MediaKeySession.generateRequest()

LayoutTests/media/encrypted-media/encrypted-media-playback-multiple-sessions.html

Index: LayoutTests/media/encrypted-media/encrypted-media-playback-multiple-sessions.html
diff --git a/LayoutTests/media/encrypted-media/encrypted-media-playback-multiple-sessions.html b/LayoutTests/media/encrypted-media/encrypted-media-playback-multiple-sessions.html
index 10963c77df23f7308dea0758997fe2d10fd0b4a7..4737ffe6cdfeadda6085e64f36fe9ceefffb9185 100644
--- a/LayoutTests/media/encrypted-media/encrypted-media-playback-multiple-sessions.html
+++ b/LayoutTests/media/encrypted-media/encrypted-media-playback-multiple-sessions.html
@@ -30,16 +30,18 @@
                 function onNeedKey(event)
                 {
                     var keyId = String.fromCharCode.apply(null, event.initData);
-                    video.mediaKeys.createSession(event.contentType, event.initData).then(function(newSession) {
+
+                    var mediaKeySession = video.mediaKeys.createSession();
+                    waitForEventAndRunStep('message', mediaKeySession, onMessage, test);
+                    mediaKeySession.generateRequest(event.contentType, event.initData).then(function() {
                         if (keyId == videoKeyId) {
                             assert_equals(videoMediaKeySession, null);
-                            videoMediaKeySession = newSession;
+                            videoMediaKeySession = mediaKeySession;
                         } else {
                             assert_equals(keyId, audioKeyId);
                             assert_equals(audioMediaKeySession, null);
-                            audioMediaKeySession = newSession;
+                            audioMediaKeySession = mediaKeySession;
                         }
-                        waitForEventAndRunStep('message', newSession, onMessage, test);
                     }).catch(function(error) {
                         forceTestFailureFromPromise(test, error);
                     });