DevTools: focus on node after editing as html

This patch brings focus to Elements tree outline after editing a node
so that one can use arrow keys to continue navigation through dom tree.

BUG=

Review URL: https://chromiumcodereview.appspot.com/23532014

git-svn-id: svn://svn.chromium.org/blink/trunk@156992 bbb929c8-8fbe-4397-9dbb-9b2b20218538