UI: A11y: ChromeVox triggers error callback in demo app

[joeyparrish]

Have you read the FAQ and checked for duplicate open issues?
Yes

What version of Shaka Player are you using?
master

Can you reproduce the issue with our latest release version?
N/A: no UI in v2.4.x

Can you reproduce the issue with the latest code from master?
yes

Are you using the demo app or your own custom app?
demo

What browser and OS are you using?
ChromeOS

What are the manifest and license server URIs?
N/A

What did you do?
Activate ChromeVox screen reader by pressing Ctrl-Alt-Z

What did you expect to happen?
No errors

What actually happened?
Although ChromeVox activates and works, somehow, one of our error handlers is triggered and we display the error "goog.require could not find: cvox.ApiImplementation" in the demo app.

[joeyparrish]

This handler is being triggered:

  // Display uncaught exceptions.
  window.addEventListener('error', function(event) {
    shakaDemo.onError_(/** @type {!shaka.util.Error} */ (event.error));
  });