Rebaseline XMLHttpRequest tests for Mac 10.6

BUG=
TBR=mkwst@chromium.org

Review URL: https://codereview.chromium.org/166443006

git-svn-id: svn://svn.chromium.org/blink/trunk@167366 bbb929c8-8fbe-4397-9dbb-9b2b20218538