一个incoming call的流程 （来电话代码流程）

1. 创建GsmPhone时，mCT = new GsmCallTracker(this);
2. 创建GsmCallTracker时:
    cm.registerForCallStateChanged(this, EVENT_CALL_STATE_CHANGE, null); -->    
    mCallStateRegistrants.add(r); 
3. RIL中的RILReceiver线程首先读取从rild中传来的数据：processResponse -> processUnsolicited
4. 对应于incoming call,RIL收到RIL_UNSOL_RESPONSE_CALL_STATE_CHANGED 消息，触发mCallStateRegistrants中的所有记录。
5. GsmCallTracker处理EVENT_CALL_STATE_CHANGE，调用pollCallsWhenSafe
6. 函数pllCallsWhenSafe 处理：
     lastRelevantPoll = obtainMessage(EVENT_POLL_CALLS_RESULT);
     cm.getCurrentCalls(lastRelevantPoll);
7. RIL::getCurrentCalls
    RILRequest rr = RILRequest.obtain(RIL_REQUEST_GET_CURRENT_CALLS, result);
    ...
    send(rr);
8. 接着RIL调用processSolicited处理RIL_REQUEST_GET_CURRENT_CALLS的返回结果
9. GsmCallTracker的handleMessage被触发，处理事件EVENT_POLL_CALLS_RESULT,调用函数  
    handlePollCalls
10. handlPollCalls 调用
    phone.notifyNewRingingConnection(newRinging);

11. PhoneApp中创建CallNotifier
12. CallNotifier注册：
    registerForNewRingingConnection -> mNewRingingConnectionRegistrants.addUnique(h, what, obj);