DevTools: Don't handle touch event twice while in inspect mode.

This fixes a regression introduced in r152542.

BUG=245046
TEST=manual
R=apavlov@chromium.org

Review URL: https://codereview.chromium.org/18721004

git-svn-id: svn://svn.chromium.org/blink/trunk@154646 bbb929c8-8fbe-4397-9dbb-9b2b20218538