The standard viewer implicitly depends on the `onPassword` and `onProgress` callbacks, in order to open password protected PDF files, respectively to report file loading progress. We currently have no unit-tests for this functionality, which seems unfortunate; hence this patch.
*Please note:* Rather than adding more unit-tests to `api_spec.js`, I slightly extended/reworked two existing tests. Specifically for the password test, this *does not* really change what we actually test, just how the test is done.