DevTools: support //# sourceMappingURL and //# sourceURL at a time.

BUG=362994
R=alph@chromium.org

Review URL: https://codereview.chromium.org/237263002

git-svn-id: svn://svn.chromium.org/blink/trunk@171565 bbb929c8-8fbe-4397-9dbb-9b2b20218538