Refactor filereader_error.html.
Mark manual tests as manual.
Refactor filereader_readAsArrayBuffer.html.
Refactor filereader_readAsDataURL.html.
Refactor filereader_readAsText.html.
Make the UTF-16 test in filereader_readAsText.html more strict.
Refactor filereader_readystate.html.
Refactor filereader_result.html.