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 
"123 0 obj\n" +
              "<< /Type /Annot /Subtype /Widget /FT /Btn /Ff 32768 " +
              "/AP << /N << /Checked 314 0 R /Off 271 0 R>>>> " +
              "/Parent 456 0 R /AS /Checked /M (date)>>\nendobj\n"
          );
          expect(parentData.ref).toEqual(Ref.get(456, 0));
          expect(parentData.data).toEqual(
            "456 0 obj\n<< /V /Checked /Kids [123 0 R]>>\nendobj\n"
          );
          return annotation;
        }, done.fail)
        .then(annotation => {
          const annotationStorage = {};
          annotationStorage[annotation.data.id] = { value: false };
          return annotation.save(partialEvaluator, task, annotationStorage);
        }, done.fail)
        .then(data => {
          expect(data).toEqual(null);
          done();
        }, done.fail);
    });
    it("should save radio buttons without a field value", function (done) {
      const appearanceStatesDict = new Dict();
      const normalAppearanceDict = new Dict();
      normalAppearanceDict.set("Checked", Ref.get(314, 0));
      normalAppearanceDict.set("Off", Ref.get(271, 0));
      appearanceStatesDict.set("N", normalAppearanceDict);
      buttonWidgetDict.set("Ff", AnnotationFieldFlag.RADIO);
      buttonWidgetDict.set("AP", appearanceStatesDict);
      const buttonWidgetRef = Ref.get(123, 0);