Usage of imgIDecoderObserver Interface

 Start the load and decode of an image.
 @param aURI the URI to load
 @param aInitialDocumentURI the URI that 'initiated' the load -- used for 3rd party cookie blocking
 @param aReferrerURI the 'referring' URI
 @param aLoadGroup Loadgroup to put the image load into
 @param aObserver the observer
 @param aCX some random data
 @param aLoadFlags Load flags for the request
 @param aCacheKey cache key to use for a load if the original
                  image came from a request that had post data
 @param aRequest A newly created, unused imgIRequest object or NULL for one to
                     be created for you.


 libpr0n does NOT keep a strong ref to the observer; this prevents
 reference cycles.  This means that callers of loadImage should
 make sure to Cancel() the resulting request before the observer
 goes away.

[noscript] imgIRequest loadImage(in nsIURI aURI, in nsIURI aInitialDocumentURL, in nsIURI aReferrerURI, in nsILoadGroup aLoadGroup, in imgIDecoderObserver aObserver, in nsISupports aCX, in nsLoadFlags aLoadFlags, in nsISupports cacheKey, in imgIRequest aRequest)

 Start the load and decode of an image.
 @param aChannel the channel to load the image from.  This must
                 already be opened before ths method is called, and there
                 must have been no OnDataAvailable calls for it yet.   
 @param aObserver the observer
 @param cx some random data
 @param aListener [out]
        A listener that should receive the data. Can be null, in which
        case imagelib has found a cached image and is not interested in
        the data. The caller needs not cancel the channel in this case.

 libpr0n does NOT keep a strong ref to the observer; this prevents
 reference cycles.  This means that callers of loadImageWithChannel should
 make sure to Cancel() the resulting request before the observer goes away.

[noscript] imgIRequest loadImageWithChannel(in nsIChannel aChannel, in imgIDecoderObserver aObserver, in nsISupports cx, out nsIStreamListener aListener)

 Clone this request; the returned request will have aObserver as the
 observer.  aObserver will be notified synchronously (before the clone()
 call returns) with all the notifications that have already been dispatched
 for this image load.

imgIRequest clone(in imgIDecoderObserver aObserver)

 Used to register an image decoder observer.  Typically, this will
 be a proxy for a frame that wants to paint the image.
 Notifications from ongoing image loads will be passed to all
 registered observers.  Notifications for all request types,
 current and pending, will be passed through.

 @param aObserver the observer to register

 @throws NS_ERROR_OUT_OF_MEMORY

void addObserver(in imgIDecoderObserver aObserver)

 Used to unregister an image decoder observer.

 @param aObserver the observer to unregister

void removeObserver(in imgIDecoderObserver aObserver)