function ItemDragPlaceholder(item) {
    this._item = item;
    this._animation = new Animator();
    this._element = null;
    this._className = '';
    this._didMigrate = false;
    this._resetAfterLayout = false;
    this._left = 0;
    this._top = 0;
    this._transX = 0;
    this._transY = 0;
    this._nextTransX = 0;
    this._nextTransY = 0;

    // Bind animation handlers.
    this._setupAnimation = this._setupAnimation.bind(this);
    this._startAnimation = this._startAnimation.bind(this);
    this._updateDimensions = this._updateDimensions.bind(this);

    // Bind event handlers.
    this._onLayoutStart = this._onLayoutStart.bind(this);
    this._onLayoutEnd = this._onLayoutEnd.bind(this);
    this._onReleaseEnd = this._onReleaseEnd.bind(this);
    this._onMigrate = this._onMigrate.bind(this);
    this._onHide = this._onHide.bind(this);
  }
Drag placeholder.

@class
@param {Item} item