nsIUnicharStreamLoaderObserver Interface

 Called when the first full segment of data if available.

 @param aLoader the unichar stream loader
 @param aContext the context parameter of the underlying channel
 @param aFirstSegment the raw bytes of the first full data segment
 @param aLength the length of aFirstSegment

 @return charset corresponding to this stream

 @note this method will only be called if the stream loader receives an
       OnDataAvailable call.

ACString onDetermineCharset(in nsIUnicharStreamLoader aLoader, in nsISupports aContext, [size_is(aLength)] in string aFirstSegment, in unsigned long aLength)

 Called when the entire stream has been loaded.

 @param aLoader the unichar stream loader
 @param aContext the context parameter of the underlying channel
 @param aStatus the status of the underlying channel
 @param aUnicharData the unichar input stream containing the data.  This
        can be null in some failure conditions.

 This method will always be called asynchronously by the
 nsUnicharIStreamLoader involved, on the thread that called the
 loader's init() method.

 @note If the stream loader does not receive an OnDataAvailable call,
       aUnicharData will be null, and aStatus will be a success value.

void onStreamComplete(in nsIUnicharStreamLoader aLoader, in nsISupports aContext, in nsresult aStatus, in nsIUnicharInputStream aUnicharData)