imgIDecoderObserver Interface

 called when some part of the frame has new data in it

[noscript] void onDataAvailable(in imgIRequest aRequest, in gfxIImageFrame aFrame, [const] in nsIntRect aRect)

 called once the image has been inited and therefore has a width and height

void onStartContainer(in imgIRequest aRequest, in imgIContainer aContainer)

 called as soon as the image begins getting decoded

void onStartDecode(in imgIRequest aRequest)

 called when each frame is created

void onStartFrame(in imgIRequest aRequest, in gfxIImageFrame aFrame)

 called at the same time that nsIRequestObserver::onStartRequest would be
 (used only for observers of imgIRequest objects, which are nsIRequests,
 not imgIDecoder objects)

 Unlike nsIRequestObserver::onStartRequest, this can be called
 synchronously.

void onStartRequest(in imgIRequest aRequest)

 probably not needed.  called right before onStopDecode

void onStopContainer(in imgIRequest aRequest, in imgIContainer aContainer)

 called when the decoder is dying off

void onStopDecode(in imgIRequest aRequest, in nsresult status, in wstring statusArg)

 called when a frame is finished decoding

void onStopFrame(in imgIRequest aRequest, in gfxIImageFrame aFrame)

 called at the same time that nsIRequestObserver::onStopRequest would be
 (used only for observers of imgIRequest objects, which are nsIRequests,
 not imgIDecoder objects)

 Unlike nsIRequestObserver::onStartRequest, this can be called
 synchronously.

void onStopRequest(in imgIRequest aRequest, in boolean aIsLastPart)