Improve accessibility: alert on error.

[shivbijlani]

Update gutter.js to allow assistive technology to announce an error when it occurs in a row.

[nightwing]

Are you sure this improves accessibility? It announces errors randomly while typing and scrolling, which makes reading of the code harder.

[shivbijlani]

Thanks for taking a look @nightwing . Without this, there is no way to know if what you have typed in the editor is incorrect. If you can't see the red X in the gutter, then you cant hover over it. Which means there is no way to see the error message tooltip. A better fix would be to show the error message in an element that is always visible so that the low vision user can tab to it. That is a larger design change.

The accessibility best practice for error messages that popup is to announce them with role="alert".