DevTools: keyboard navigation broken in the viewported Network panel

BUG=403430
R=eustas@chromium.org, lushnikov@chromium.org

Review URL: https://codereview.chromium.org/468043004

git-svn-id: svn://svn.chromium.org/blink/trunk@180245 bbb929c8-8fbe-4397-9dbb-9b2b20218538