Used to test https://bugs.webkit.org/show_bug.cgi?id=25475
Load the Web Inspector and look at the script's panel, and the script list drop-down control. You should see entries for scripts named "(program):f0.js" through "(program):f12.js". The entries were named via proper use of the //@sourceURL comment. There will also be entries named "(program)" for source that does not properly use, or use at all, the //@sourceURL comment.
Now, set a breakpoint in the body of the "f0" function in the "(program):f0.js" script. Then click this button:
When stopped at the breakpoint, the entry for the function in the call stack control should the name of the script, "(program):f0.js", beside the function name "f0". Note the function name for f0 is set with the new "displayName" property.