function KeyframeNode(spatialNode, keyframe) {
  this.spatialNode = spatialNode;
  this.keyframe = keyframe;
  this.state = LoadState.UNLOADED;
  this.content = undefined;
  this.megatextureIndex = -1;
  this.priority = -Number.MAX_VALUE;
  this.highPriorityFrameNumber = -1;
}
@alias KeyframeNode
@constructor

@param {SpatialNode} spatialNode
@param {number} keyframe

@private