Timeline: make TimelinePresentationModel._linkifyScriptLocation() never return null

_linkifyScriptLocation() could previously return null if the details were not specified.
The result could be accidently misused, so make details mandatory and use _linkifyLocation()
when there's no default details.

R=apavlov@chromium.org

Review URL: https://codereview.chromium.org/106183003

git-svn-id: svn://svn.chromium.org/blink/trunk@163252 bbb929c8-8fbe-4397-9dbb-9b2b20218538