message: Fix resize error when using canvas as root
diff: // mainLayer.resize(width, height);
  layers[0] = mainLayer;
  zlevelList.push(0);
  +
  + this._domRoot = root;
  }
  this.pathToImage = this._createPathToImage();
  * @return {HTMLDivElement}
  */
  getViewportRoot: function () {
  - return this._singleCanvas ? this._layers[0].dom : this._domRoot;
  + return this._domRoot;
  },
  /**
  