Layout test inspector/device-emulation/device-emulation-320-2x.html is not flaky anymore.

BUG=409580
TBR=pfeldman

Review URL: https://codereview.chromium.org/720613003

git-svn-id: svn://svn.chromium.org/blink/trunk@185387 bbb929c8-8fbe-4397-9dbb-9b2b20218538