DevTools: Allow JavaScriptSourceFrame to decide when to perform live edit.

This patch exposes commitLiveEdit on the ScriptFile.

R=pfeldman

Review URL: https://codereview.chromium.org/238163007

git-svn-id: svn://svn.chromium.org/blink/trunk@171573 bbb929c8-8fbe-4397-9dbb-9b2b20218538