code: function () {
                  /** @type {?} */
                  var canvas = this.canvas.nativeElement;
                  /** @type {?} */
                  var ctx = canvas.getContext('2d');
                  ctx.clearRect(0, 0, this.dimensions.width, this.dimensions.height);
              }
docs: clears the shape canvas
  @private
  @return {?}