Add additional layout tests for MediaKeySession.keyStatuses

LayoutTests/media/encrypted-media/encrypted-media-keystatuses-multiple-sessions-expected.txt

 EVENT(message)
 EVENT(keystatuseschange)
 for (var entry of keyStatuses)
 123, usable
+for (var key of keyStatuses.keys())
+123
+for (var value of keyStatuses.values())
+usable
+for (var entry of keyStatuses.entries())
+123, usable
+keyStatuses.forEach()
+123, usable
+EVENT(message)
+EVENT(keystatuseschange)
+for (var entry of keyStatuses)
 4567890, usable
 for (var key of keyStatuses.keys())
-123
 4567890
 for (var value of keyStatuses.values())
 usable
-usable
 for (var entry of keyStatuses.entries())
-123, usable
+4567890, usable
+keyStatuses.forEach()
 4567890, usable
 This is a testharness.js-based test.
-PASS Verify MediaKeySession.keyStatuses. 
+PASS Verify MediaKeySession.keyStatuses with multiple sessions. 
 Harness: the test ran to completion.