Mark some http/tests/xmlhttprequest/ tests as failing

They appear to be failing benignly (printing 0 rather than null), but we
should do try to understand why before just blindly rebaselining.

BUG=369730
TBR=jam,tfarina

Review URL: https://codereview.chromium.org/264003002

git-svn-id: svn://svn.chromium.org/blink/trunk@173252 bbb929c8-8fbe-4397-9dbb-9b2b20218538