DevTools: settings to switch on/off autocompletion and bracket matching

This patch adds settings to enable/disable text editor autocompletion
and bracket matching.

BUG=308863
R=vsevik@chromium.org

Review URL: https://codereview.chromium.org/32413002

git-svn-id: svn://svn.chromium.org/blink/trunk@160148 bbb929c8-8fbe-4397-9dbb-9b2b20218538