Fix issue where filename is default.

With Chrome 35, the method we used for the filename isn't working anymore. This pull request makes it work.

See  https://code.google.com/p/chromium/issues/detail?id=375634 about the issue and the fix.

More about Blobs: https://developer.mozilla.org/en-US/docs/Web/API/Blob.

about createObjectURL: https://developer.mozilla.org/en-US/docs/Web/API/URL.createObjectURL