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

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

Index: LayoutTests/media/encrypted-media/encrypted-media-keystatuses-multiple-sessions.html
diff --git a/LayoutTests/media/encrypted-media/encrypted-media-keystatuses-multiple-sessions.html b/LayoutTests/media/encrypted-media/encrypted-media-keystatuses-multiple-sessions.html
index bcf0fcc04e168371fb2bb5e272b12de9e5e0fa15..e579a1311a15595243d303787343131259be3f78 100644
--- a/LayoutTests/media/encrypted-media/encrypted-media-keystatuses-multiple-sessions.html
+++ b/LayoutTests/media/encrypted-media/encrypted-media-keystatuses-multiple-sessions.html
@@ -11,6 +11,8 @@
         <script>
             var mediaKeySession1;
             var mediaKeySession2;
+            var initDataType;
+            var initData;
 
             // Even though key ids are uint8, using printable values so that
             // they can be verified easily.
@@ -48,8 +50,7 @@
                     verifyKeyStatuses(mediaKeySession1.keyStatuses, { expected: [key1], unexpected: [key2] });
 
                     // Now trigger a message event on session2.
-                    var initDataType = getInitDataType();
-                    mediaKeySession2.generateRequest(initDataType, getInitData(initDataType)).catch(function(error) {
+                    mediaKeySession2.generateRequest(initDataType, initData).catch(function(error) {
                         forceTestFailureFromPromise(test, error);
                     });
                 }
@@ -87,10 +88,13 @@
                     test.done();
                 }
 
-                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();
                     mediaKeySession1 = mediaKeys.createSession();
                     mediaKeySession2 = mediaKeys.createSession();
 
@@ -105,7 +109,7 @@
                     waitForEventAndRunStep('keystatuseschange', mediaKeySession2, processKeyStatusesChange2, test);
 
                     // Generate a request on session1.
-                    return mediaKeySession1.generateRequest(initDataType, getInitData(initDataType));
+                    return mediaKeySession1.generateRequest(initDataType, initData);
                 }).catch(function(error) {
                     forceTestFailureFromPromise(test, error);
                 });