[DevTools] Disable touch emulation while inspect mode is on.

BUG=none
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/345063002

git-svn-id: svn://svn.chromium.org/blink/trunk@176610 bbb929c8-8fbe-4397-9dbb-9b2b20218538