Hello!

Let me know if i should have opened this issue on the [pdfjs-dist](https://github.com/mozilla/pdfjs-dist) repo but I though here would fit.

I'm using pdfjs-dist and I'm in need of some more types to be exported. I have no idea how the types end up in the dist-repo but would love to open a PR if only someone could point me in the right direction 😃 Since I was using an older version of pdfjs-dist I realize the only type I need that's not in the type defs in the latest release are _PageViewport_ from _[display/display_utils](https://github.com/mozilla/pdf.js/blob/master/src/display/display_utils.js#L153)_.
if (url.hostname === "localhost") {
          url.hostname = "127.0.0.1";
        } else if (params.url.hostname === "127.0.0.1") {
          url.hostname = "localhost";
        } else {
          pending("Can only run cross-origin test on localhost!");
        }
        params.url = url.href;
        loadingTask = getDocument(params);
        return loadingTask.promise
          .then(function (pdf) {
            return pdf.destroy();
          })
          .then(
            function () {
              expect(expectSuccess).toEqual(true);
            
            function (error) {
              if (expectSuccess) {
                
                expect(error).toEqual("There should not be any error");
              }
              expect(expectSuccess).toEqual(false);
            }
          );
      }
      function testCanLoad(filename, options) {
        return _checkCanLoad(true, filename, options);
      }
      function testCannotLoad(filename, options) {