DevTools: [CodeMirror] autocompletion based on suggestion popularity

This patch changes suggestions order to be sorted from the most popular
to the less popular in the file.

BUG=

Review URL: https://chromiumcodereview.appspot.com/22265005

git-svn-id: svn://svn.chromium.org/blink/trunk@155605 bbb929c8-8fbe-4397-9dbb-9b2b20218538