DevTools: Focus visible console on Ctrl+`

Currently, the hidden console is shown on Ctrl+`, but it is not focused if it is visible. This patch handles the focusing part.

R=eustas@chromium.org, eustas, vsevik
BUG=144943

Review URL: https://codereview.chromium.org/162553005

git-svn-id: svn://svn.chromium.org/blink/trunk@167592 bbb929c8-8fbe-4397-9dbb-9b2b20218538