DevTools: Reuse _showSourceLocation for execution line changes handling in sources panel.

R=lushnikov@chromium.org, lushnikov, pfeldman

Review URL: https://codereview.chromium.org/203433002

git-svn-id: svn://svn.chromium.org/blink/trunk@169555 bbb929c8-8fbe-4397-9dbb-9b2b20218538