Use requestMediaKeySystemAccess() to check type support in EME layout tests

LayoutTests/media/encrypted-media/encrypted-media-async-creation-with-gc.html

Index: LayoutTests/media/encrypted-media/encrypted-media-async-creation-with-gc.html
diff --git a/LayoutTests/media/encrypted-media/encrypted-media-async-creation-with-gc.html b/LayoutTests/media/encrypted-media/encrypted-media-async-creation-with-gc.html
index 77487aaadf602b3574cfc2b9b65153ce436a02ce..0193d95a9d27686958a0086d325cd3ebc10a57bc 100644
--- a/LayoutTests/media/encrypted-media/encrypted-media-async-creation-with-gc.html
+++ b/LayoutTests/media/encrypted-media/encrypted-media-async-creation-with-gc.html
@@ -14,13 +14,18 @@
                 // Run garbage collection often.
                 setInterval(asyncGC, 0);
 
+                var initDataType;
+                var initData;
                 var mediaKeySession;
-                navigator.requestMediaKeySystemAccess('org.w3.clearkey', [{}]).then(function(access) {
+                getSupportedInitDataType().then(function(type) {
+                    initDataType = type;
+                    initData = getInitData(initDataType);
+                    return navigator.requestMediaKeySystemAccess('org.w3.clearkey', [{}]);
+                }).then(function(access) {
                     return access.createMediaKeys();
                 }).then(function(mediaKeys) {
-                    var initDataType = getInitDataType();
                     mediaKeySession = mediaKeys.createSession();
-                    return mediaKeySession.generateRequest(initDataType, getInitData(initDataType));
+                    return mediaKeySession.generateRequest(initDataType, initData);
                 }).then(function() {
                     return mediaKeySession.close();
                 }).then(function(result) {