LayoutTests: http/tests/inspector/network/network-xhr-replay.html is slow

TBR=
BUG=

Review URL: https://codereview.chromium.org/223223002

git-svn-id: svn://svn.chromium.org/blink/trunk@170730 bbb929c8-8fbe-4397-9dbb-9b2b20218538