DevTools: inspector.js should not handle keydown event before bubbling.

R=pfeldman@chromium.org, pfeldman

Review URL: https://codereview.chromium.org/137613006

git-svn-id: svn://svn.chromium.org/blink/trunk@165417 bbb929c8-8fbe-4397-9dbb-9b2b20218538