DevTools: Add iOS 7 to list of overrides

This patch adds iOS 7 to the list of possible overrides.

BUG=275228
TBR=pfeldman

Review URL: https://codereview.chromium.org/25292002

git-svn-id: svn://svn.chromium.org/blink/trunk@158822 bbb929c8-8fbe-4397-9dbb-9b2b20218538