# File lib/ruby-debug/event_processor.rb, line 19
     def at_breakpoint(context, breakpoint)
       raise "@last_breakpoint supposed to be nil. is #{@last_breakpoint}" if @last_breakpoint
       # at_breakpoint is immediately followed by #at_line event in
       # ruby-debug-base. So postpone breakpoint printing until #at_line.
       @last_breakpoint = breakpoint
     end