function Clock () {
    this._time = 0;
    this._frame = 0;
    this._timerQueue = [];
    this._updatingIndex = 0;

    this._scale = 1;
    this._scaledTime = this._time;
}
Equivalent of an Engine in the Worker Thread. Used to synchronize and manage
time across different Threads.

@class  Clock
@constructor
@private