WebFrameTest.FirstFrameNavigationReplacesHistory is flaky

BUG=310347
TBR=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/34473005

git-svn-id: svn://svn.chromium.org/blink/trunk@160266 bbb929c8-8fbe-4397-9dbb-9b2b20218538