In the following spots a "MouseUp" eventName is being used, which does look inconsistent considering that the "Mouse Down"/"Mouse Enter"/"Mouse Exit" eventNames all have a space in them.
Is this inconsistency actually expected, or is it a simple typo? If the former, then a comment explaining *why* would be appropriate; otherwise we should just fix this :-)

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L806

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L945

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1034

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1168

/cc @calixteman 
case AnnotationType.SQUARE:
        return new SquareAnnotationElement(parameters);
      case AnnotationType.CIRCLE:
        return new CircleAnnotationElement(parameters);
      case AnnotationType.POLYLINE:
        return new PolylineAnnotationElement(parameters);
      case AnnotationType.CARET:
        return new CaretAnnotationElement(parameters);
      case AnnotationType.INK:
        return new InkAnnotationElement(parameters);
      case AnnotationType.POLYGON:
        return new PolygonAnnotationElement(parameters);
      case AnnotationType.HIGHLIGHT:
        return new HighlightAnnotationElement(parameters);
      case AnnotationType.UNDERLINE:
        return new UnderlineAnnotationElement(parameters);
      case AnnotationType.SQUIGGLY:
        return new SquigglyAnnotationElement(parameters);
      case AnnotationType.STRIKEOUT:
        return new StrikeOutAnnotationElement(parameters);
      case AnnotationType.STAMP:
        return new StampAnnotationElement(parameters);
      case AnnotationType.FILEATTACHMENT:
        return new FileAttachmentAnnotationElement(parameters);
      default:
        return new AnnotationElement(parameters);
    }
  }
}
class AnnotationElement {