Add xhr.response for 'arraybuffer' responseType.

[hackerwins]

The responseType property of the XMLHttpRequest object can be set to change the expected response type from the server.

This patch can receive binary data from server with xhr.response.

for more details about sending and receiving binary data. https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Sending_and_Receiving_Binary_Data