/**
 * internalSave: Used when saving a document or URL.
 *
 * If aChosenData is null, this method:
 *  - Determines a local target filename to use
 *  - Prompts the user to confirm the destination filename and save mode
 *    (aContentType affects this)
 *  - [Note] This process involves the parameters aURL, aReferrer (to determine
 *    how aURL was encoded), aDocument, aDefaultFileName, aFilePickerTitleKey,
 *    and aSkipPrompt.
 *
 * If aChosenData is non-null, this method:
 *  - Uses the provided source URI and save file name
 *  - Saves the document as complete DOM if possible (aDocument present and
 *    right aContentType)
 *  - [Note] The parameters aURL, aDefaultFileName, aFilePickerTitleKey, and
 *    aSkipPrompt are ignored.
 *
 * In any case, this method:
 *  - Creates a 'Persist' object (which will perform the saving in the
 *    background) and then starts it.
 *  - [Note] This part of the process only involves the parameters aDocument,
 *    aShouldBypassCache and aReferrer. The source, the save name and the save
 *    mode are the ones determined previously.
 *
 * @param aURL
 *        The String representation of the URL of the document being saved
 * @param aDocument
 *        The document to be saved
 * @param aDefaultFileName
 *        The caller-provided suggested filename if we don't 
 *        find a better one
 * @param aContentDisposition
 *        The caller-provided content-disposition header to use.
 * @param aContentType
 *        The caller-provided content-type to use
 * @param aShouldBypassCache
 *        If true, the document will always be refetched from the server
 * @param aFilePickerTitleKey
 *        Alternate title for the file picker
 * @param aChosenData
 *        If non-null this contains an instance of object AutoChosen (see below)
 *        which holds pre-determined data so that the user does not need to be
 *        prompted for a target filename.
 * @param aReferrer
 *        the referrer URI object (not URL string) to use, or null
 *        if no referrer should be sent.
 * @param aSkipPrompt [optional]
 *        If set to true, we will attempt to save the file to the
 *        default downloads folder without prompting.
 *        When this function is called, directly or indirectly, by Mozilla
 *        Archive Format to save a file automatically, this parameter can also
 *        be an object with the following properties:
 *         - saveDir: nsILocalFile instance pointing to the directory where the
 *           specified document should be saved. The filename is determined
 *           automatically, using "index" as the basename.
 *         - saveWithMedia: If true, the Save Complete persist object is
 *           configured to save the media files that are present in the page.
 *         - saveWithContentLocation: If true, the Save Complete persist object
 *           is configured to save the page for inclusion in an MHTML file.
 *         - mafEventListener: Object implementing the onSaveNameDetermined,
 *           onDownloadComplete, and onDownloadFailed event functions. The
 *           persistObject property may also be set on the object.
 *        When this function is called, directly or indirectly, by Mozilla
 *        Archive Format to ask the user to save an archive, this parameter can
 *        also be an object with the following properties:
 *         - mafAskSaveArchive: True to ask to save archives only.
 *         - mafSaveTabs [optional]: Array of browser objects corresponding to
 *           the tabs to be saved.
 *        When this function is called, directly or indirectly, by Mozilla
 *        Archive Format to create an archive automatically, this parameter can
 *        also be an object with the following properties:
 *         - targetFile: nsIFile of the final destination page or archive.
 *         - saveBehavior: Save behavior to use when creating the file.
 *         - mafProgressListener: Object implementing the nsIWebProgressListener
 *           interface, used to detect when the operation completes.
 * @param aCacheKey [optional]
 *        If set will be passed to saveURI.  See nsIWebBrowserPersist for
 *        allowed values.
 */
function internalSave(aURL, aDocument, aDefaultFileName, aContentDisposition,
                      aContentType, aShouldBypassCache, aFilePickerTitleKey,
                      aChosenData, aReferrer, aSkipPrompt, aCacheKey)