... at least for the function which will remain after restructuring of
the debug interface. For some methods that will be removed anyway, we
just return zero / null for now.

I also refactored the ScriptLocationFromLine method to make it more
readable and reuse parts in other files (like ScriptLinePosition).

BUG=5655
R=titzer@chromium.org, jgruber@chromium.org

Review-Url: https://codereview.chromium.org/2512833003
Cr-Commit-Position: refs/heads/master@{#41115}