DevTools: Trim sourceURL from scripts before showing them in the editor

BUG=249259
R=pfeldman_ooo, apavlov

Review URL: https://codereview.chromium.org/93663006

git-svn-id: svn://svn.chromium.org/blink/trunk@164311 bbb929c8-8fbe-4397-9dbb-9b2b20218538