DevTools: Use in JavaScriptSourceFrame current target's debuggerModel instead of WebInspector.debuggerModel

BUG=

Review URL: https://codereview.chromium.org/355823002

git-svn-id: svn://svn.chromium.org/blink/trunk@177036 bbb929c8-8fbe-4397-9dbb-9b2b20218538