Improve TypeError messages from failed array conversions.

LayoutTests/fast/events/init-message-event-expected.txt

Index: LayoutTests/fast/events/init-message-event-expected.txt
diff --git a/LayoutTests/fast/events/init-message-event-expected.txt b/LayoutTests/fast/events/init-message-event-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..c03f450f2bedd6ba05fd06ebec6fde749c1a3c0f
--- /dev/null
+++ b/LayoutTests/fast/events/init-message-event-expected.txt
@@ -0,0 +1,12 @@
+Checks that initMessageEvent() is working
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS newEvent.initMessageEvent("message", true, true, "ff", "*", 43, window, {x:1}); threw exception TypeError: 8th argument is neither an array, nor does it have indexed properties..
+PASS newEvent.initMessageEvent("message", true, true, "ff", "*", 43, window, null) did not throw exception.
+PASS [object MessageEvent] is an instance of function MessageEvent() { [native code] }
+PASS successfullyParsed is true
+
+TEST COMPLETE
+