An nsIChannelClassifier object checks a channel's URI against the
 URI classifier service, and cancels the channel before OnStartRequest
 if it is found on a blacklist.
[scriptable, uuid(1481c5b5-9f6e-4995-8fe3-2aad5c06440d)]
interface nsIChannelClassifier : nsISupports

Methods

 Cancel an existing query.  If a channel has been suspended, it will
 be resumed.
void cancel() 
 Notify the classifier that the channel was redirected.  The new channel
 will be suspended pending a new classifier lookup.

 @param aOldChannel
        The channel that's being redirected.
 @param aNewChannel
        The new channel. This channel is not opened yet.
void onRedirect(in nsIChannel aOldChannel, in nsIChannel aNewChannel) 
 Checks a channel against the URI classifier service (if it exists).

 The channel will be suspended while the classifier is checked.  The
 channel may be cancelled with an error code determined by the classifier
 before it is resumed.

 If there is no URI classifier service, NS_ERROR_FACTORY_NOT_REGISTERED
 will be returned.

 This method must be called immediately after AsyncOpen() has been called
 on the channel.

 @param aChannel
        The channel to suspend.
 @param aInstallListener
        If true, the classifier will install notification
        callbacks to listen for redirects.  The classifier will
        pass all notifications on to the channel's existing
        notification callbacks.
void start(in nsIChannel aChannel, in boolean aInstallListener)