question: public void addBridgeIdleDebugListener ( NotThreadSafeBridgeIdleDebugListener listener ) { mBridgeIdleListeners . add ( listener ) ; }
target:  Adds a idle listener for this Catalyst instance. The listener will receive notifications whenever the bridge transitions from idle to busy and vice-versa, where the busy state is defined as there being some non-zero number of calls to JS that haven't resolved via a onBatchCompleted call. The listener should be purely passive and not affect application logic.