Implement MediaKeySession.generateRequest()

LayoutTests/media/encrypted-media/encrypted-media-v2-events.html

Index: LayoutTests/media/encrypted-media/encrypted-media-v2-events.html
diff --git a/LayoutTests/media/encrypted-media/encrypted-media-v2-events.html b/LayoutTests/media/encrypted-media/encrypted-media-v2-events.html
index 10323dbd657b3d43309eccf8bb0afd5443477579..637b4bae98a08dde9f724033d39b75f4e9c4c77f 100644
--- a/LayoutTests/media/encrypted-media/encrypted-media-v2-events.html
+++ b/LayoutTests/media/encrypted-media/encrypted-media-v2-events.html
@@ -24,10 +24,9 @@
 
                 MediaKeys.create('org.w3.clearkey').then(test.step_func(function(mediaKeys) {
                     var initDataType = getInitDataType();
-                    return mediaKeys.createSession(initDataType, getInitData(initDataType));
-                })).then(test.step_func(function(result) {
-                    mediaKeySession = result;
+                    var mediaKeySession = mediaKeys.createSession();
                     waitForEventAndRunStep('message', mediaKeySession, test.step_func(processMessage), test);
+                    return mediaKeySession.generateRequest(initDataType, getInitData(initDataType));
                 })).catch(test.step_func(function(error) {
                     forceTestFailureFromPromise(test, error);
                 }));