Comment 292 for bug 195698

Honza, could you please write a (short) comment that answers the question:
  "What is the purpose of class PromptAggregator and what mechanism
  does it use to achieve it?"
(and add that comment near the class definition)

Proposed test: Say you have two Firefox windows open. In one window you use "open group of tabs bookmark". This group of tab requires two different password prompts. With your patch one prompt is now queued. The first prompt comes up. Now you say "firefox quit" in the other window. What will happen? When the first prompt gets closed, will your new code open the second prompt window and block exit?