DevTools: allow sortRange to sort arbitrary range of an array

Previously it was able to sort first elements only.

R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/23637006

git-svn-id: svn://svn.chromium.org/blink/trunk@157605 bbb929c8-8fbe-4397-9dbb-9b2b20218538