startDrawingMode(mode, option) {
    if (this._isSameDrawingMode(mode)) {
      return true;
    }

    // If the current mode is not 'NORMAL', 'stopDrawingMode()' will be called first.
    this.stopDrawingMode();

    const drawingModeInstance = this._getDrawingModeInstance(mode);
    if (drawingModeInstance && drawingModeInstance.start) {
      drawingModeInstance.start(this, option);

      this._drawingMode = mode;
    }

    return !!drawingModeInstance;
  }
Start a drawing mode. If the current mode is not 'NORMAL', 'stopDrawingMode()' will be called first.
@param {String} mode Can be one of <I>'CROPPER', 'FREE_DRAWING', 'LINE', 'TEXT', 'SHAPE'</I>
@param {Object} [option] parameters of drawing mode, it's available with 'FREE_DRAWING', 'LINE_DRAWING'
 @param {Number} [option.width] brush width
 @param {String} [option.color] brush color
@returns {boolean} true if success or false