Right-click in the left gutter of a Script view (with line numbers) - only the "Inspect Element" item is present in the context menu. Thus, it is not possible to modify or add a conditional breakpoint.
In the console log for the Inspector, the following error occurs:
Uncaught TypeError: Cannot call method 'bind' of undefined (TextViewer:294)
Created attachment 140500 [details]
Committed r116293: <http://trac.webkit.org/changeset/116293>