Android 左右滑屏，實作Back按鍵

左右滑屏，實作Back按鍵

思路：
	1.下拉快捷彈框如何實作，input事件處理
	2.back按鈕事件接口調用
           

下拉分發事件代碼路徑：

• /frameworks/base/services/core/java/com/android/server/wm/WindowManagerService.java
• frameworks/base/services/core/java/com/android/server/wm/RootWindowContainer.java
• frameworks/base/services/core/java/com/android/server/wm/DisplayContent.java
• frameworks/base/services/core/java/com/android/server/wm/DisplayPolicy.java
• /frameworks/base/services/core/java/com/android/server/wm/SystemGesturesPointerEventListener.java

SystemGesturesPointerEventListener.java

@Override
public void onPointerEvent(MotionEvent event) {
    if (mGestureDetector != null && event.isTouchEvent()) {
        mGestureDetector.onTouchEvent(event);
    }
    switch (event.getActionMasked()) {
        case MotionEvent.ACTION_DOWN:
            mSwipeF