Test for bug 34653: XMLHttpRequest should force to send content-type as charset equals UTF-8.

Test1 (setRequestHeader was not called): FAILURE: 'text/plain;charset=UTF-8 '
Test2 (setRequestHeader was called without a charset): SUCCESS
Test3 (setRequestHeader was called with a non-UTF8 charset): SUCCESS
Test4 (setRequestHeader was called with multiple charsets and other attributes): SUCCESS