Improve handling of JS functions with empty URLs.
Improve handling of JS functions with empty URLs.

Some JS functions have an empty URL but non-empty line and column information (e.g. wrapObject, InjectedScript.RemoteObject).
Give them a non-empty resource and filename so that it doesn't say ':23:153' but rather '<unknown>:23:153'.

mstange/cleopatra,devtools-html/perf.html,devtools-html/perf.html,mstange/cleopatra