豆瓣电台笔记2：增加暂停/恢复歌曲的时候同时停止/恢复唱片上的动画

    //MARK: 暂停layer上的动画
    func pauseLayer(layer: CALayer) {
        let pausedTime: CFTimeInterval = layer.convertTime(CACurrentMediaTime(), fromLayer: nil)
        layer.speed = 0.0
        layer.timeOffset = pausedTime
    }
    
    //MARK: 继续layer上的动画
    func resumeLayer(layer: CALayer) {
        let pausedTime = layer.timeOffset
        layer.speed = 1.0
        layer.timeOffset = 0.0
        layer.beginTime = 0.0
        let timeSincePause = layer.convertTime(CACurrentMediaTime(), fromLayer: nil) - pausedTime
        layer.beginTime = timeSincePause
    }