Update test expectations with XHR test that has become flaky after recent changes.

TBR=kouhei@chromium.org
NOTRY=true
BUG=417181

Review URL: https://codereview.chromium.org/593383004

git-svn-id: svn://svn.chromium.org/blink/trunk@182572 bbb929c8-8fbe-4397-9dbb-9b2b20218538