bug - Mat-chip-list - has incorrect aria role when empty

[chrisbubernak]

Bug, feature request, or proposal:

Bug: elements with "listbox" role require children "option" role but an empty mat-chip-list is still a "listbox".

What is the expected behavior?

Not sure what the best solution is but my guess would be that mat-chip-list should have a different role when it has no children. Normally the mat-chip-list should have chips but there could be situations where the mat-chip-list starts empty and has chips dynamically added.

What is the current behavior?

Currently mat-chip-list's role is always "listbox".

What are the steps to reproduce?

Providing a StackBlitz/Plunker (or similar) is the best way to get the team to see your issue.

Plunker starter (using on @master): https://goo.gl/DlHd6U

StackBlitz starter (using latest npm release): https://goo.gl/wwnhMV

What is the use-case or motivation for changing an existing behavior?

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Is there anything else we should know?

[naomiblack]

This is one of the issues turned up in our aXe testing.

[angular-automatic-lock-bot]

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