nsIPrintingPrompt in Firefox 3.6a1pre

  Shows the print progress dialog

  @param printSettings - PrintSettings for page setup (required)
  @param aObs - An observer to know if the contents of the Print Settings 
                object has changed while the dialog is being shown. 
                For example, some platforms may implement an "Apply" button (not required)

  This service enables embedders to implement their own Print and Progress Dialogs.
  Each platform has a "base" or "basckstop" implementation of the service. The 
  service is automatically registered at start up.

  Historically, platform toolkits with native dialogs have implemented them in the GFX layer
  Usually they were displayed when a new DeviceContextSpec specific to that platform
  was created.

  Windows: The GFX layer no longers supports default toolkit behavior for displaying the 
           native Print Dialog.
           If an embedder implemented service returns any error code (other than NS_ERROR_ABORT)
           printing will terminate.

           Returning NS_OK assumes that the PrintSettings object was correctly filled in and
           if it does not have valid fields for printer name, etc. it may also terminate.

           Defaults for platform service:           
             showPrintDialog       - displays a native dialog
             showPageSetup         - displays a XUL dialog
             showProgress          - displays a XUL dialog
             showPrinterProperties - n/a

           Summary for Windows Embedders:
             Stated once again: There is no "fallback" native platform support in GFX for the
             displaying of the native print dialog. The current default implementation for Windows
             display a native print dialog but a XUL-based progress dialog.
             If you wish to have a native progress dialog on Windows you will have to create and 
             register your own service.
  
             Note: The Windows version Mozilla implements this service which is 
                   automatically built and registered for you. You can use it as an example.
                   It is located at "mozilla/embedding/components/printingui/src/win". That service
                   is capable of displaying a native print dialog and a XUL progress dialog.

             To fly your own dialog you may:

              1) Implement this service to display at least the Print Dialog and a Print Progress Dialog
                 or you may implement just one of the dialogs and pass back NS_ERROR_NOT_IMPLEMENTED
                 for any of the others.

              2) For the Print Dialog:
                 You may stub out this service by having all the methods return NS_ERROR_NOT_IMPLEMENTED.
                 You can then fly you own dialog and then properly fill in the PrintSettings object
                 before calling nsIWebBrowserPrint's Print method. If you stub out this service  
                 you MUST set "printSilent" to true, if you do not, Printing will terminate and an 
                 error dialog will be displayed.

  Mac: The GFX layer still supports default toolkit behavior for displaying the Print Dialog.
       If an embedder implemented service returns NS_ERROR_NOT_IMPLEMENTED for "showPrintDialog"
       The toolkit will display the native print dialog.

       Defaults for platform service:           
       Mac OS9: showPrintDialog       - displays a native dialog
                showPageSetup         - displays a native dialog
                showProgress          - displays a XUL dialog
                showPrinterProperties - n/a
                
       Mac OSX: showPrintDialog       - displays a native dialog
                showPageSetup         - displays a native dialog
                showProgress          - not implemented (provided by OS)
                showPrinterProperties - n/a
                
  GTK: There are no native dialog for GTK.

       Defaults for platform service:           
         showPrintDialog       - displays a XUL dialog
         showPageSetup         - displays a XUL dialog
         showProgress          - displays a XUL dialog
         showPrinterProperties - displays a XUL dialog
              
  OS2: 

       Defaults for platform service:           
         showPrintDialog       - displays a XUL dialog
         showPageSetup         - displays a XUL dialog
         showProgress          - displays a XUL dialog
         showPrinterProperties - displays a native dialog
              



  Show the Print Dialog 

  @param webBrowserPrint - represents the document to be printed
  @param printSettings - PrintSettings for print "job"

  Sometimes platforms need to bring up a special properties dialog for showing
  print specific properties. Although the PrintSettings has a place to set the 
  printer name, here is is an argument to be clear as to what printer is being
  asked to have the properties set for it. The Printer name in the PS is ignored.

  @param printerName - name of printer (required)
  @param printSettings - PrintSettings for page setup (required)

  Shows the print progress dialog

  @param webBrowserPrint - represents the document to be printed
  @param printSettings - PrintSettings for print "job"
  @param openDialogObserver - an observer that will be notifed when the dialog is opened
  @param isForPrinting - true - for printing, false for print preview
  @param webProgressListener - additional listener can be registered for progress notifications
  @param printProgressParams - parameter object for passing progress state
  @param notifyOnOpen - this indicates that the observer will be notified when the progress
                        dialog has been opened. If false is returned it means the observer
                        (usually the caller) shouldn't wait
                        For Print Preview Progress there is intermediate progress